An Exploratory Estimation of the Willingness to Pay for and Perceptions of Nature-Based Therapy for Cardiovascular Diseases

Abstract

There is increasing evidence of the benefits of natural environments for human health. Interest is growing in nature-based therapy (NBT), organised initiatives that promote human–nature interactions with the aim of achieving positive health outcomes. Although the benefits of spending time in nature are now widely recognised, the public’s perspective of NBTs is still not well understood nor quantified. At the same time, chronic non-communicable diseases such as cardiovascular disease are on the rise, increasing costs and pressure for public health services. Using a sample of 96 respondents in Italy, this exploratory study investigates the economic value and perceptions of an NBT for cardiovascular disease. We employed the contingent valuation method to estimate marginal willingness to pay (WTP) for a nature-based rehabilitation programme compared to a standard indoor clinic-based programme. Logistic regression was used to estimate median WTP and influencing factors. We investigated the preferences of patients for the features and potential benefits of nature-based rehabilitation. We show that patients with cardiovascular disease in Italy have a positive WTP between EUR 14.01 to EUR 42.69 per day (median value EUR 27.26). Our findings indicate that NBTs could offer a promising alternative to standard indoor programmes. We provide recommendations for designing NBTs based on the preferences of our sample, aiming to contribute to sustainable health and land management policies.

1. Introduction

Despite economic growth and overall gains in standards of living, as modern industrialised societies become more urbanised, digitalised and detached from the natural world, an increasing prevalence of lifestyle-related health issues has emerged [1,2,3]. Cancers, cardiovascular diseases and chronic respiratory diseases now rank among the leading causes of death worldwide, with this trend expected to continue [4]. This shift in disease burden towards non-communicable long-term diseases [5], with a primary contribution of cardiovascular disease, is leading to increasing economic costs and global pressure for public health services [6]. This situation requires attention from two different angles: research and policy.

On the one hand, research increasingly recognises natural environments’ potential to alleviate these health concerns [7]. Numerous studies indicate that spending time in nature offers a multitude of health benefits. Initiatives and programmes that actively connect people with nature with the intention of achieving positive health outcomes are known as ‘nature-based intervention’ (NBI) or ‘nature-based therapy’ (NBT). Nature exposure can be beneficial for human health through a variety of pathways, such as providing restorative environments for mental recovery, encouraging social connections and physical activity and reducing exposure to air, noise and heat pollution, e.g., [8,9,10,11,12]. Interventions that address human health and wellbeing while incorporating interaction with nature are growing in popularity [13,14,15,16]. This can be observed in programmes across various high-income countries such as green social prescribing in the United Kingdom [17], the park prescription programme PaRX in Canada [18] and national policies promoting “shinrin-yoku” (forest bathing) in Japan [19] or forest therapy in Korea [20]. In addition, recent research has focused on the role of nature-based therapies specifically targeting cardiovascular disease [21,22].

On the other hand, studies estimating the economic value of such interventions are less common [23,24], tend to be more present in the non-peer-reviewed “grey literature” [14] and face methodological shortcomings. For example, very few studies so far have employed conventional valuation methods, e.g., willingness to pay (WTP), indicating a need for more comprehensive and robust economic evaluations [23]. If the application of robust economic valuation methods, particularly WTP, can demonstrate positive monetary values for the health benefits of NBTs, these estimates could be a powerful decision-support tool justifying investments and policy reforms to support these interventions and guide future implementation. Additionally, it is important to consider individual perceptions and attitudes towards these programmes, which can significantly influence future uptake [15]. Beyond promoting sustainable human health and wellbeing, these interventions involve changes to land use and management practices [15,25] and require integrating health objectives into environmental planning. We believe that complementing current knowledge on the health effects of NBIs with information about their economic value and public preferences will help advance both research and policy.

Given this, the present study takes an exploratory approach with two main aims. Firstly, it applies the contingent valuation (CV) method, which is frequently applied to both health and environmental issues, to estimate WTP values for a nature-based rehabilitation programme for cardiovascular disease. Secondly, it investigates the perceptions, knowledge and preferences of patients with cardiovascular disease about the nature-based programme. Based on these findings, we provide recommendations for both health and environmental policies, two sectors that have traditionally operated in isolation [26]. This paper is structured as follows: The Materials and Methods Section describes the data collection and contingent valuation method. The Results Section presents the main findings about WTP for a nature-based rehabilitation programme for cardiovascular disease, and the perceptions, knowledge and preferences of patients. The Discussion Section highlights reflections for sustainable environmental management and health policies and compares the results with the existing literature. Lastly, our key findings are summarised in the Conclusions Section.

2. Nature-Based Therapy: Theory, Potential and Economic Evaluation

Nature-based therapy (NBT) is an approach to health programmes that incorporates nature exposure into the therapeutic process [27]. There is a wide range of different interventions that utilise nature in the achievement of health goals, and consequently, there exists a variety of different terms to describe them [28,29]. NBT is also referred to as eco-therapy, nature-based health interventions, green care, nature-assisted therapy and nature therapy. For the purposes of this study, we use the term NBT, defined as a subset of nature-based interventions featuring a structured element of therapy for specific illnesses. The therapeutic use of the natural environment is founded on the idea that human health and wellbeing are intrinsically linked with nature. This concept is based on the following theories, for the most part originating from psychology: The Biophilia Hypothesis states that humans have an innate affiliation to nature based on evolutionary factors [30]. This spurred research into the idea that our relationship with nature is a key component of good health. The Attention Restoration Theory (ART) suggests that spending time in nature can help replenish cognitive resources, in particular attention, by providing restorative environments and “soft fascination” (e.g., from observing features of nature) [31]. The Stress Reduction Theory (SRT) proposes that viewing or spending time in nature can immediately reduce physiological and psychological stress [32]. This theory claims that humans’ psychological responses to natural environments are positive, and that even passive nature exposure can reduce stress levels compared to exposure to urban environments.

These perspectives all emphasise the therapeutic benefits that interacting with nature could have for human health. Further studies show that nature not only benefits emotional and mental wellbeing but can promote increased levels of physical activity [33]. Visiting green spaces once a week has been shown to significantly increase the likelihood of meeting recommended levels of physical activity [34]. For this reason, NBTs have the potential to improve the health of patients with cardiovascular disease. NBTs have been shown to have positive effects on both psychological and physical health and reduce disease symptoms across different patient groups [28]. Moreover, research suggests that outdoor exercise can increase quality of life, reduce mental stress [35] and lead to increased positive feelings when compared to indoor exercise [36]. Therefore, NBTs could be a promising alternative to standard indoor therapy, promoting sustainable and resilient citizen health.

As mentioned previously, compared to studies on the health effects of NBT, there is a lack of research economically evaluating NBT, particularly through the use of WTP. To the best of our knowledge, there are no other studies estimating WTP for an NBT for cardiovascular disease. The closest study we have identified is by Lee et al. [37], who estimated the WTP for access to a horticulture therapy site in South Korea. They estimated WTP with the CV method to be EUR 225.85170 per month (euro values presented here are the authors’ elaboration of original studies’ estimates converted to current euro prices using an inflation calculator and average yearly exchange rates). This points towards substantial economic value if such interventions are implemented in South Korea. However, they recommend treating these results with caution, and warn against extrapolating outside of the specific sample. Other similar studies exist, although generally with a wider focus on nature-based interventions (NBIs) and not on a specific therapy or rehabilitation. Pretty et al. [7] undertook an economic evaluation of three NBIs and one mindfulness-based intervention in the UK. They assessed the costs and benefits of the interventions and indicate a substantial economic value based on changes in life satisfaction which were linked with reduced loneliness and doctor visits. However, this analysis lacks robustness as the calculations of the costs are not clear, nor are they calculated for all four interventions. Similarly, the estimation and valuation of the benefits are scarcely described and are calculated based on the increases in life satisfaction recorded, without any control group for comparison. Busk et al. [23] share our concerns over these issues, and hence, we believe that there is need for more robust and focused research on this topic. Hartfield et al. [38] used social return on investment (SROI) to evaluate the economic impact of several NBIs such as bushcraft, woodland walks and mindfulness. Using costs and a social value calculator, they indicate that the interventions provide a positive social value ratio. However, the study provides valuation estimates based on previous wellbeing estimates and does not undertake any primary valuation exercise itself. Willis et al. [39] use cost-effectiveness analysis to assess the economic impacts of group-based woodland activities for individuals with mental health problems. They estimate value based on the improvements in quality-adjusted life years. Their results indicate, again, a substantial value for these interventions; however, the analysis is based on many underlying assumptions and the results should hence be treated with caution. All of these studies indicate the potential for NBT to provide significant economic benefits to participants. However, the heterogeneity in methods employed and lack of robust methods suggest that further research is needed, concurrent with the findings of [23]. Additionally, only one study implemented conventional non-market valuation methods such as WTP, indicating a clear opportunity to enhance the existing literature through the application of this approach to NBT.

3. Materials and Methods

We applied the contingent valuation (CV) method to estimate WTP for a nature-based rehabilitation programme (i.e., a nature-based therapy (NBT)) for cardiovascular disease in Italy. CV is a stated preference method that elicits monetary values for non-market goods [40]. It is necessary when there is a lack of data on market transactions. Through survey questions, CV estimates monetary values by asking respondents their WTP for a hypothetical change in the provision of a good or service. By creating a hypothetical market scenario, the method aims to elicit responses that represent how people would behave in a real market situation, therefore producing values that reflect genuine economic choices. In this study, WTP acts as a measure of perceived value for a specific type of nature-based therapy targeting patients with cardiovascular disease, representing both the direct and indirect benefits provided by it. Despite the well-acknowledged limitations of the CV method, such as hypothetical bias [41], it was deemed suitable for our study given the specific focus on estimating monetary values for a programme that is not currently available but, in the future, could be offered to patients in the health market. Therefore, hypothetical bias should be reduced in this context as the good is somewhat familiar to respondents and substitutes exist [42]. As a result, it may be easier for respondents to imagine the scenario as if it were real and to express their true WTP accordingly. Moreover, as previously mentioned, the CV method is commonly applied in both the environmental [43] and health [44] fields to value the benefits of future programmes. Nature-based interventions or therapies can be conceptualised as a combination of both environmental and health goods, and thus we suggest that the CV method is appropriate for this valuation. In this section, we present the following: how the survey was administered (Section 3.1), designed and structured (Section 3.2); how the scenarios were developed and presented to respondents (Section 3.3); the elicitation of WTP (Section 3.4); techniques used to minimise biases (Section 3.5); how the survey was implemented (Section 3.6); and the empirical strategy followed (Section 3.7).

3.1. Survey Administration

A web-based questionnaire was administered using LimeSurvey, the platform used by the University of Padova for online surveys [45]. Although face-to-face interviews have been recommended for CV surveys [46], newer studies indicate that internet-based methods can produce comparable WTP estimates and are now increasingly employed given their advantages for survey design [47,48,49]. They are considered a cost-effective way of reaching our target population while enabling randomisation of the surveys and the use of visual aids.

3.2. Survey Design and Structure

The survey and valuation scenario were designed in several iterative steps and following best-practice guidelines [46,50]. After extensive collaboration with four medical experts, the hypothetical scenario for a nature-based rehabilitation programme and survey questions were developed and pre-tested. The final questionnaire contained four sections. In the first section, questions focused on spending time in nature, knowledge of nature-based therapies, perceived risks and other factors shown in the literature to influence WTP for health and nature-based interventions [51,52,53]. Respondents’ perceptions were collected from questions using a 5-level Likert scale and other multiple-choice questions. In the second section, respondents were presented with the WTP hypothetical scenario of a rehabilitation programme offered to patients with cardiovascular disease, and follow-up questions to check comprehensibility and identify protest answers. In the third section, respondents’ demographic and socio-economic information was collected. In the final (optional) section, we asked respondents’ opinions on the different features of a nature-based therapy programme and the potential benefits, in order to formulate recommendations for environmental and health policy. The survey was in Italian, targeting Italians at risk of or experiencing cardiovascular disease.

3.3. Scenario Description and Payment Vehicle

As the CV method relies on responses to a hypothetical market scenario, it is crucial to keep the described scenario as realistic as possible [54]. Therefore, in the WTP section, also developed in the Italian language, respondents were first introduced to information on the current prevalence of cardiovascular disease in Europe and the benefits of cardiac rehabilitation programmes. Next, they were provided with information on the benefits of nature exposure for human health, and the potential to integrate outdoor exercises and nature into rehabilitation programmes. This aimed to provide respondents with more comprehensive information about nature-based therapies, in order to enable them to make informed willingness-to-pay decisions. Subsequently, respondents were presented with two scenarios: firstly the current status quo of an indoor clinic-based cardiac rehabilitation programme, and secondly, a novel offer of an outdoor nature-based programme. This follows recommendations by Johnston et al. [50] to reduce risks of overinflated WTP values by clearly presenting respondents with both a status quo and a change scenario to be valued. This forces respondents to consider two alternatives in unison, hence reducing “budget constraint bias” [55,56].

Table 1. Conventional indoor clinic-based and innovative outdoor nature-based rehabilitation scenarios presented to respondents (source: own elaboration).

	Indoor Clinic-Based Rehabilitation	Outdoor Nature-Based Rehabilitation
Activities:	Description:
Aerobic exercise	Walking on a treadmill in a training room	Guided walks outdoors in nature
Guided strength training	In a training room using resistance bands and gym machines	Outdoors in nature in a suitably chosen exercise space in areas such as parks, forests or mountainous areas using resistance bands and body weight
Guided relaxation exercises	In a training room	Outdoors in a suitably chosen exercise space
Guided balance and flexibility exercises	In a training room	Outdoors in a suitably chosen exercise space
Programme aim:
	To reduce disease symptoms and return patients back to the best level of independent functioning possible post heart transplant or exacerbation (similar to standard cardiac rehabilitation).	To reduce disease symptoms and return patients back to the best level of independent functioning possible post heart transplant or exacerbation while taking advantage of the benefits of physical exercise and direct contact with nature. To encourage and give patients the skills and knowledge to continue with exercises outdoors once the programme ends.

summarises the details of the two programmes presented to respondents. Respondents were informed that the therapy methods and safety precautions of both programmes are comparable, but that in the nature-based rehabilitation, all activities were conducted outdoors in nature, with the aim of harnessing the synergetic benefits of physical activity and spending time in nature [12]. The scenarios were enriched with visual aids in the form of photographs depicting the two possible programmes. Respondents were then asked to indicate which option they would choose between the two alternatives.

Subsequently, and regardless of their answer to the previous question, respondents were asked if they would be willing to pay a certain amount, per day, to undertake the nature-based instead of the clinic-based rehabilitation programme, hence eliciting their marginal WTP for the nature-based option. The CV question, originally in Italian, read

“Cardiac rehabilitation is usually offered in a hospital or clinic setting. Suppose that the nature-based rehabilitation is more costly than the clinic/hospital programme, as it is a new and innovative therapy offering, and that the extra costs would have to be paid for with your own money. Would you be willing to pay €X extra (out of your own pocket, in addition to any co-payment you may currently have to pay) per day to undertake the nature-based rehabilitation instead of the indoor clinic-based programme?”

Given the health context, we opted for an out-of-pocket payment vehicle to assess the programme value from a patient perspective. Moreover, this approach was considered more realistic as it is likely that if the therapy was to become available in the future, patients would bear some of the costs themselves. Feedback from medical experts and pre-testing informed our temporal choice of a daily payment.

3.4. Elicitation of WTP

Our study elicited WTP using a double-bounded dichotomous choice (DBDC) approach, which, building on a single-bounded dichotomous choice approach, asks a follow-up WTP question to the initial WTP question. The DBDC, unlike the open-ended or payment-card approaches, has the methodological benefit of being incentive-compatible and offers improved statistical efficiency over the single-bounded approach, especially with smaller samples [50,57,58]. Firstly, respondents were presented with the first bid, A1, and asked if they would be willing to pay this amount to undertake the nature-based instead of the clinic-based rehabilitation programme. Following pilot testing using a payment-card approach, four starting bid values were identified (namely, EUR 10, 20, 30, 100 per day) and assigned at random to respondents via the Limesurvey platform. Following this, and depending on whether respondents answered yes or no to the first bid, they were presented with the follow-up WTP question. If respondents answered ‘yes’ to A1, the question was repeated with a higher amount: A2 = 2(A1) (i.e., EUR 20, 40, 60, 200 per day). If respondents answered ‘no’ to A1, they were presented with a lower bid: A3 = 1/2(A1) (i.e., EUR 5, 10, 15, 50 per day). This sequence of questions generates four possible answer combinations—‘yes–yes’, ‘yes–no’, ‘no–yes’ and ‘no–no’—enabling the estimation of an individual’s true WTP from the range defined by the higher and lower bid values.

Table 2. Relationship between WTP for person i and bid values presented in our survey.

Answer to Initial Bid (A1)	Answer to Follow-Up Bid
	Yes	No
Yes	WTPi > A2	A1< WTPi < A2
No	A1 > WTPi >A3	WTPi < A3

illustrates the relation between an individual’s WTP and the initial and follow-up bids, where A3 < A1 < A2.

3.5. Empirical Strategy

Our approach follows random utility theory, which assumes that individuals will choose to maximise their utility between given alternatives; thus, the preferred alternative is that which provides the highest utility [59].

Therefore, we can derive the indirect utility function of individual i (U_i) as

$$U_i=v\left(y_i,NBT\right)+{\epsilon }_i$$

where $v\left(\text{-}\right)$ is the deterministic component of utility, $y_i$ is income, NBT is a binary variable representing the presence or absence of a nature-based therapy and ${\epsilon }_i$ is the random component of utility (error term).

Subsequently, a respondent accepts the bid if the cost is less than the utility they will receive from the proposal, i.e., if they are better off paying the cost A and accepting the proposal for the NBT compared to not paying:

$$U\left(y_i-A,{NBT}_1\right)+{\epsilon }_{i1}\ge U\left(y_i,{NBT}_0\right)+{\epsilon }_{i2}$$

where ${NBT}_1$ represents the situation where the NBT is implemented (at cost A) and ${NBT}_0$ is the current situation with no NBT implemented and no extra cost. Therefore, the probability of accepting the WTP bid is

$$P\left(Yes\right)=P[v\left(y_i-A,{NBT}_1\right)+{\epsilon }_i^1\ge v\left(y_i,{NBT}_0\right)+{\epsilon }_i^2$$

Accordingly, the probability of accepting the bid is therefore equal to 1 minus the probability that WTP is less than the bid:

$$P\left(WTP\right)\ge A=1-F(A;\theta )$$

where $F(A;\theta )$ is the logistic cumulative distribution function of WTP for bid value A, and $\theta$ represents the parameters to be estimated. In a DBDC approach, where respondents are presented with both an initial and a follow-up bid, the likelihood function is defined according to the response probability of the four possible outcome intervals as follows:

$$P\left(YY\right)=P(A2\le WTPi<\mathrm{\infty })$$

$$P\left(YN\right)=P(A1\le WTPi<\mathrm{A}2)$$

$$P\left(NY\right)=P(\mathrm{A}3\le WTPi<\mathrm{A}1)$$

$$P\left(NN\right)=P(0\le WTPi<A3)$$

where YY is the possible combination of answers ‘yes–yes’ to the double-bounded dichotomous choice applied in the survey. Similarly, the others are, respectively, ‘yes–no’, ’no–yes’ and ‘no–no’. Given this, we estimated a logit model using a maximum likelihood estimator in the “DCchoice” package in R studio [60]. DCchoice is a built-in package developed specifically by [61] for analysing DBDC data, rendering it a suitable tool for the analysis of our survey data. Accordingly, we estimated the following log-likelihood function:

$$\begin{array}{l} \mathit{ln}\left(L\right)={\sum }_{i=1}^N[d_i^{yy}\mathit{ln}\left(1-F\left(A_{2i};\theta \right)\right)+d_i^{yn}\mathit{ln}\left(F\left(A_{2i};\theta \right)-F\left(A_{1i};\theta \right)\right)+\\ d_i^{ny}\mathit{ln}\left(F\left(A_{1i};\theta \right)-F\left(A_{3i};\theta \right)\right)+d_i^{nn}\mathit{ln}\left(F\left(A_{3i};\theta \right)\right)]\end{array}$$

where $d_i$ is a dummy variable indicating respondent i’s answer pattern to the first and second bids, i.e., one of the four answer combinations, such as yes to the first bid and yes to the second bid. The estimated coefficients from this regression are then used to calculate median WTP for the sample, which is defined as follows:

$$MedianWTP=-{\displaystyle \frac{{\beta }_0}{{\beta }_1}}$$

where ${\beta }_0$ is the constant, and ${\beta }_1$ is the bid coefficient from the estimated logit model.

We first estimated median WTP using a simple model including only the bid variable. Next, we tested additional specifications including other covariates such as age, gender and other personal factors such as past experience and knowledge of NBTs and perceived risks/benefits to assess if they significantly influence WTP. This was carried out following a hierarchical approach, in which different variables were added one by one to the regression, and their effect and significance were evaluated. The final models presented in the Section 4 include the variables found to be statistically significant and standard controls. This process and variable selection were guided by economic theory and evidence in the literature on factors that may affect WTP for health interventions and nature-based therapies [51,52,53]. The results are presented in the following section, including significant variables, median WTP and confidence intervals.

3.6. Measures to Mitigate Risks of Potential Biases

In order to mitigate the risks of hypothetical bias, the valuation question was proceeded by a “cheap talk” script, reminding respondents to consider their income and budget constraints and of the tendency of respondents to misstate their true WTP in these hypothetical scenarios. This has been shown to effectively reduce biases in previous CV studies [62]. To reduce comparison bias and sequencing effects, we first presented respondents with the clinic-based programme followed by the nature-based programme. This order was chosen to prevent respondents from developing a preference for the nature-based option simply because it was introduced first. By maintaining this sequence, we aimed to ensure that any preference for the nature-based programme was genuine rather than a result of scenario ordering. Additionally, the scenario description was enriched with visual aids, which has been shown to increase reliability in WTP estimates [63]. Debriefing questions allowed us to identify any respondents who gave problematic responses, for example, those who stated to have not understood the willingness-to-pay questions or who answered randomly. Identifying and removing these respondents from the analysis of the WTP answers results in more reliable estimates that should better reflect genuine preferences.

3.7. Survey Implementation

The survey was conducted from December 2024 to February 2025, employing a convenience sampling method. Leveraging the authors’ connections within the Cardiac Surgery Unit at the University of Padua, Italy, the questionnaire was distributed to approximately 400 individuals. The target respondents were Italians from various regions of the country who either suffered from advanced heart failure or had undergone heart transplantation. These individuals had received medical and surgical treatment at the University Hospital in Padua and were thus in regular contact with cardiac doctors.

4. Results

In this section, first we present basic descriptive statistics about respondents’ profiles and characteristics (Section 4.1), then we describe the knowledge, perceptions and preferences of respondents about nature-based rehabilitation (Section 4.2) and finally we report the model results and estimated WTP values (Section 4.3).

4.1. Respondents’ Descriptive Statistics

In total, we collected 104 completed responses to the questionnaire, a response rate of approximately 26%. A total of 6 respondents who indicated that they did not have cardiovascular disease were excluded, leaving 98 for analysis (see

Table 3. Profile of patients with cardiovascular disease.

Characteristic	Level	Frequency (%)
Age	18–29	3 (3.06)
	30–39	7 (7.14)
	40–49	5 (5.10)
	50–59	21 (21.43)
	60–69	27 (27.55)
	Over 70	33 (33.67)
	No answer	2 (2.04)
Gender	Female	29 (29.59)
	Male	69 (70.41)
Education	Primary school	6 (6.12)
	Middle school	27 (27.55)
	High school	49 (50.00)
	Bachelor degree	3 (3.06)
	Master degree	11 (11.22)
	Specialised post master degree	2 (2.04)
Monthly income	Less than EUR 600	6 (6.12)
	Between EUR 600 and EUR 1249	25 (25.51)
	Between EUR 1250 and EUR 1669	16 (16.33)
	Between EUR 1670 and EUR 2499	13 (13.27)
	Between EUR 2500 and EUR 3339	1 (1.02)
	Between EUR 3340 and EUR 4169	4 (4.08)
	Between EUR 4170 and EUR 4999	4 (4.08)
	Between EUR 5000 and EUR 5839	2 (2.04)
	Between EUR 5840 and EUR 7500	2 (2.04)
	Above EUR 7500	4 (4.08)
	No answer	21 (21.43)
Level of cardiovascular disease	At risk but no symptoms	60 (61.22)
	Structural heart disease but no symptoms	13 (13.27)
	Current or previous symptoms of heart failure	4 (4.08)
	Don’t know/unspecified	21 (21.43)
Participated in past cardiac rehabilitation	Yes	44 (44.89)
Perceived need for rehabilitation	Very unlikely	23 (23.47)
	Unlikely	35 (35.71)
	Likely	34 (34.69)
	Very likely	6 (6.12)

). Our sample contained more males (70%) than females (30%), and most respondents were in the age range of 60–70+. The majority of respondents completed high school (50%), while a lower percentage have obtained a university degree (16%). In terms of occupation, 38 respondents are employed, 4 are unemployed, and the remaining 55 are classified as retired, students, looking after their family home or undertaking voluntary activities. The median monthly income estimated using the mid-point method was EUR 1474.5 (the median value is reported given the presence of four respondents who reported very high monthly incomes (above EUR 7500); it should be noted that 21% of our sample did not answer the income question). The majority of our sample is classified as at risk of cardiovascular disease, defined as having undergone a heart transplant, hypertension, coronary vascular disease, diabetes, obesity, exposure to cardiotoxic agents or genetic variants/a family history of cardiovascular disease. A smaller proportion (4%) suffers from more advanced levels of the disease. Almost half (44.9%) of the sample stated that they had already participated in a cardiac rehabilitation programme in the past. Moreover, most respondents do not perceive a large risk with regard to their current condition, approximately 60% think it is unlikely that they will need to undertake rehabilitation in the next 2 years, and the average score for self-rated health was 68 out of 100.

4.2. Knowledge, Perceptions and Preferences About Nature-Based Rehabilitation

The results of the first section of the questionnaire revealed that the vast majority of respondents have never taken part in a nature-based intervention (93%) and have a limited knowledge on the topic (81%). However, in general, respondents display positive attitudes towards them, with 82% choosing the nature-based programme over the indoor option. Most respondents agree that spending time in nature benefits health (see Appendix A) and can encourage pro-environmental behaviours. The majority of respondents agreed that outdoor exercise should be utilised for the treatment of cardiovascular disease and that nature-based therapies are safe. Respondents demonstrated relatively lower agreement with the statement on nature-based therapies being backed up by enough science (mean 3.57). Another important attitudinal finding is that an overwhelming majority believe that the State should pay for nature-based therapies.

Table 4. Attitudes towards nature-based therapy (NBT) for cardiovascular disease.

Statements Evaluated on a 5-Point Likert Scale	Mean (sd)
Outdoor exercise should be utilised for cardiovascular disease	4.40 (0.68)
NBT can be dangerous for cardiovascular disease	2.14 (1.3)
NBT is backed up by enough science	3.57 (0.99)
NBT should be paid for by the State	3.82 (1.15)

Note: sd = standard deviation; the 5-point Likert scale ranged from 1 = fully disagree to 5 = fully agree.

displays some of these findings.

The results from the final optional section provide information on respondents’ preferences for the features of a nature-based therapy and perceptions on the potential benefits (see Appendix B for details of statements presented), providing us with relevant information for health and environmental policy. Given the length of this section, which contained 25 statements, a four-point scale was chosen to produce answers with a clear divide between important and unimportant features. This approach aimed to reduce the likelihood of cursory neutral responses and encourage thorough engagement. Here the Likert scale had values of 1 = not important at all, 2 = not important, 3 = quite important and 4 = very important. With regard to feature preferences, the most valued were a clean, well-maintained outdoor environment (mean 3.75) and safety (area checked for environmental hazards: mean 3.39). Accessibility also ranked highly (mean 3.3), which was defined in the questionnaire as a location being easily reachable within a 1 h drive from home. The less important features provide other insights into respondents’ preferences. Wilderness experience, which was defined as a location in unspoilt nature and far from the respondent’s home, was rated as the least important (mean 2.57), followed by the possibility of undertaking the therapy alone (mean 2.7) and crowds in the area (mean 2.87). Regarding environmental features, respondents highly valued the presence of large trees and high plant diversity and placed (relatively) less importance on the presence of animals and waterbodies and a mountainous location. Figure 1 displays these findings.

In terms of the relative importance of the potential benefits of a nature-based therapy for cardiovascular disease, we observed additional attitudes. In general, respondents rated quite highly all the potential benefits, with the lowest rating given to the benefits associated with social connections (meeting other people with cardiovascular disease: mean 2.96; increasing social connections in general: mean 3.05) and connecting with nature (mean 3.28). This mirrors what we observed in the feature preferences, where the option to undertake therapy alone was not highly rated. What seem to be more important to our sample are the direct health benefits, such as the reduction in disease risk factors (mean 3.65), increased ability and motivation to self-manage the disease (mean 3.51 and 3.55, respectively) and the reduction in anxiety and stress (mean 3.61). Figure 2 displays these findings.

4.3. Regression Results and WTP Estimates

Two respondents were excluded from the WTP analysis due to misunderstanding the WTP question or providing random answers, resulting in a total sample of 96 observations for this part of our analysis. In general, the bid response data conform to expectations based on economic theory. Figure 3 shows that the percentage of YY answers for the lowest bid vector (EUR 5/10/20) is much higher than for the highest bid vector (EUR 50/100/200). A similar inversed pattern is observed for the percentage of NN answers, indicating that as the bid price increases, acceptance generally falls. Conversely, the bid vector of EUR 20 has a much higher percentage of NN answers compared to the higher bid vector of EUR 100. This is likely due to the lower number of respondents being randomly assigned to this group of bids. The randomisation process inherent in the LimeSurvey platform resulted in an uneven distribution of the bid amounts. The starting bids of EUR 10, EUR 20, EUR 30 and EUR 100 were assigned to 25, 20, 28 and 23 respondents, respectively. This led to a slight underrepresentation of the starting bids of EUR 20 and EUR 100, possibly explaining such an unexpected result.

We estimated median WTP and investigated influencing factors by testing different model specifications of the log-likelihood function. Only the preferred models are presented here, for the sake of brevity (

Table 5. Preferred models: estimation of double-bounded dichotomous choice models using the maximum likelihood estimator (source: own elaboration).

Variable	Model 1	Model 2
Male		0.509
		(0.450)
Age 30–39		1.156
		(1.526)
Age 40–49		0.137
		(1.688)
Age 50–59		−0.658
		(1.430)
Age 60–69		0.427
		(1.436)
Age > 70		−0.281
		(1.390)
High-school education		0.690
		(0.468)
University degree		1.692 **
		(0.661)
Chose NBT		1.589 ***
		(0.582)
Good knowledge of NBT		1.128 **
		(0.542)
Bid	−0.025 ***	−0.030 ***
	(0.003)	(0.004)
Constant	0.675 ***	−1.613
	(0.212)	(1.472)
Log-likelihood	−151.957	−137.323
Likelihood ratio (LR) statistic	0	29.269
Degrees of freedom	0	10
p value	1	0.001
AIC	307.915	298.646
BIC	313.044	329.165
Observations	96	94
Median WTP	27.26	28.81
95% CI	EUR 14.01–EUR 42.69	EUR 6.80–EUR 48.29

*** indicates significance at the 1% level; ** significance at the 5% level. Coefficients rounded to three decimal points. CIs are confidence intervals.

): (1) a simple logit model including only a constant and the bid value, and (2) an integrated model including basic socio-demographics plus two dummy variables, one equal to 1 if the respondent chose the nature-based therapy option and another equal to 1 if they stated that they have good or excellent knowledge of nature-based therapies. In order to preserve the total number of observations and hence improve model reliability, income was excluded from our logit model due to a high proportion of missing values, which reduced the observations to only 75. The results of the additional models can be found in the Supplementary Materials. Our model results suggest that education may influence WTP, with those with a university degree showing a statistically significantly higher WTP compared to those with just basic schooling. Those who chose the outdoor nature-based rehabilitation programme instead of the indoor clinic-based option were more likely to be willing to pay more. Notably, self-reported knowledge of nature-based therapies emerged as a significant predictor of WTP. Respondents who indicated having good or excellent knowledge of nature-based therapy demonstrated a higher likelihood of being willing to pay. In contrast, variables such as age, relationship status, level of disease, self-rated health and perceived benefits/risks showed no statistically significant effects on WTP.

Confidence intervals (CIs) were calculated for median WTP based on the results of Model 1 to account for uncertainty in model estimates. The results indicate that patients with cardiovascular disease would be willing to pay between EUR 14.01 to EUR 42.69 per day (median EUR 27.26) to undertake the outdoor nature-based programme instead of the indoor clinic-based option. Figure 4 shows the estimated demand curve for the nature-based therapy. Here we can see that at a cost of EUR 27.26 per day, 50% of individuals would be willing to pay and that, as the cost increases, the probability of being WTP decreases. The relative validity of the WTP estimates is supported by respondents’ confidence in their answers, with 80% of the sample reporting that they were certain or very certain of their responses.

5. Discussion

In this section, we comment on and discuss results in relation to the identified knowledge, perceptions and preferences of respondents about nature-based therapies (Section 5.1) and the estimated WTP values (Section 5.2). In addition, we present certain considerations about our study limitations (Section 5.3) and policy recommendations (Section 5.4).

5.1. Knowledge, Perceptions and Preferences About Nature-Based Therapies

Understanding individuals’ preferences and perceptions about nature-based therapies is crucial for the possible future uptake and acceptability of these approaches to rehabilitation. Empirical information on these aspects could help both environmental and health managers in understanding the optimal design and delivery of nature-based programmes and, ultimately, potentially increasing the provision of benefits.

Our findings highlight that a portion of patients lack an adequate understanding of their disease severity. Six participants indicated they were free of cardiac pathology despite belonging to the group selected by physicians. Additionally, 21.43% of participants, while aware of having heart disease, were unable to quantify its severity (see Table 3). These results are likely driven by the issue of poor health literacy that afflicts chronic diseases, particularly in the field of heart transplantation [64].

Furthermore, with regard to nature-based therapy, our results reveal that most of our sample has limited knowledge on the topic, which could be due in part to variability in terminology. At present, there is no overall consensus on a single term or definition for nature-based therapy, with diverse terms being used for these types of interventions [29]. However, this may also reflect reality, given that only 7% of the sample reported participating in such an intervention. Therefore, these results highlight that nature-based therapies are a novel form of treatment, not currently integrated in traditional health policies in Italy. Furthermore, in line with [29], our results seem to indicate a perceived lack of scientific evidence for NBT, with this statement receiving a slightly lower average score than others. However, this points towards a discrepancy as most respondents claimed to have no or limited knowledge of NBT, and therefore, there are some doubts around the accuracy of their opinions on this, given their limited knowledge. Respondents’ answers indicate a lower importance being placed on the social aspects of interventions with respect to individual physical and mental benefits, which is noteworthy given evidence indicating that nature-based interventions can be particularly beneficial in groups [65]. This result seems to be in accordance with Bressane et al. [66] who found more scepticism with regard to the social health benefits from nature exposure. This could be explained by the fact that most scientific research has focused more on the physical and mental health benefits of spending time in nature, and thus, there is less awareness of the social health benefits. Therefore, more scientific research and increased knowledge transfer on the social benefits of nature-based rehabilitation programmes are needed.

Our study demonstrates some noteworthy findings in relation to feature preferences for nature-based therapies. Concordant with Smock et al. [29], we found that location and accessibility were highly important. Notably, we found that the most important features were a clean environment, safety precautions and being located near their home. In contrast, untouched nature in wilderness and no crowds were less important. This could reflect the fact that our study targeted a specific group of individuals with cardiovascular disease, who may highly appreciate these characteristics due to worries for their health and thus may not have a huge interest in undertaking these interventions in unspoilt and remote, mountainous natural areas where the perceived risks for their own safety could be higher. Although remoteness has been considered an important feature for the provision benefits of nature-based therapies in other countries [67,68], our results suggest that different target groups may have preferences for specific locations. Therefore, the choice of these locations cannot be standardised but, rather, should be accurately designed around the specific profile of users and beneficiaries.

Our findings show that the most important benefits are those related to disease symptoms and the self-management of the disease, while increased connectedness with nature was not highly rated. This is a noteworthy finding and could be due, again, to the specific respondents’ health condition. They may be more concerned with the immediate health benefits as they suffer from a chronic disease, and thus, benefits such as increased nature connectedness may be less perceived or considered a lower priority. Most importantly, the vast majority of respondents chose the outdoor nature-based programme over the standard indoor option, suggesting a growing societal demand to reconnect with nature and interest in these new forms of nature-based health interventions. The motivations given for being willing to pay were that 33% wanted to try this new type of rehabilitation, and 19% believed that the nature-based therapy would provide improved health benefits over the indoor option (see Appendix C). These findings indicate a growing interest in these approaches, which has important implications for healthcare but also for land-use planning where multiple and often conflicting demands come into play.

5.2. WTP for Nature-Based Therapy and Influencing Factors

Our results provide a range of welfare estimates for a nature-based rehabilitation programme for cardiovascular disease in Italy. The median WTP per day is EUR 27.26 (EUR 14.01–EUR 42.69, 95% CI). Aggregating this to a weeklong programme, we estimate a total WTP of EUR 190.82 for the nature-based therapy (EUR 98.07–EUR 298.83, 95% CI). The estimated WTP is in line with the costs of a clinic-based rehabilitation in Italy, which in the Veneto region costs EUR 20.30 per day, or EUR 142.10 a week [69]. However, the public-good nature of health services in Italy, as well as in many other European countries, means that most individuals do not directly bear the full costs of treatment, paying only a contribution, and hence may not be aware of the full costs and value of the intervention. The average WTP is higher than the costs of a standard indoor programme, indicating a substantial added value for a nature-based programme.

To the best of our knowledge, this is the first attempt at estimating the WTP for an outdoor nature-based versus indoor clinic-based therapy for patients with cardiovascular disease; thus, it is difficult to find comparison studies for our results. However, an attempt can be made to compare this study with the few studies that estimate WTP for other types of nature-based therapies. Our values seem quite high compared to Lee et al. [37], who estimated the WTP for access to a horticulture therapy site in South Korea to be EUR 225.85170 (all euro values presented here are the authors’ elaboration of original studies’ estimates converted to current euro prices using an inflation calculator and average yearly exchange rates) per month, which equates to a value of approximately EUR 7.54 per day. Gail et al. [52] estimated the WTP for a forest bathing site in the Philippines to be EUR 12.28 per visit (although with a small sample size of 60 participants). While both of these estimates initially seem considerably lower than our estimates, when we consider the relative cost of the WTP values compared to average incomes in the respective countries, we obtain more comparable results. The estimates from Lee et al. [37] correspond to a WTP of approximately 5.2% (authors’ elaboration, using average income reported in study and WTP) of the sample’s monthly income for access to the horticulture therapy site, and in Gail et al. [52], the average WTP per visit was approximately 1.8% of the monthly income (authors’ elaboration; through taking the mid-point of the studies’ middle-level income range and dividing by 12, monthly average income was calculated). Expressed as a percentage of average monthly income, our WTP of EUR 27.26 equates to roughly 1.8%. Therefore, we find that our results seem to be in line with these estimates. Shifting our focus to the health-related literature, we can compare our findings with the results of Burge et al. [70]. Albeit not specifically focused on nature-based therapy, they estimated the aggregate WTP for home-based pulmonary rehabilitation versus clinic-based rehabilitation to be EUR 58.26. The absence of a specified programme duration in their WTP scenario complicates direct comparisons with our daily WTP estimate. However, if we assume this to be a daily WTP, our estimates are within the same order of magnitude.

With regard to factors influencing WTP, contrary to previous studies, we did not find that programme experience had a significant effect on WTP [71]. This may stem from the low percentage of our sample having direct experience (7%). Furthermore, neither age, gender nor the perceived risks/benefits were found to be statistically significant as indicated by Steigenberger et al. and Gail et al. [51,52]. However, this finding is not uncommon [70] and may be due in part to the relatively limited size of our sample, potentially constraining the explanatory power of our models. This underscores the need for future research employing larger, more representative samples to further explore these relationships. Nevertheless, our results do concur with Steigenberger et al. [51] in terms of the significance observed of education and previous knowledge, which both have a positive effect on WTP. Previous knowledge is likely to influence WTP as individuals are more familiar with the described scenario and may perceive fewer associated risks, increasing WTP. According to [37], a lack of knowledge on the benefits of NBT could lead to increased variability in WTP estimates and hence should also be considered when interpreting our results as it may have affected the spread of our WTP estimates. Higher education, again, could influence WTP as those with a university degree may have a higher degree of health literacy. However, it is also likely that this trend is instead picking up some of the effects of income, as highly educated individuals tend to have higher earnings and are thus willing to pay more (models tested including the income variable show that education is no longer significant but remains positive, although our observations drop to 75 due to the large proportion of missing values). Given that our sample displayed preferences for NBT in clean natural areas close to home and with safety checks, it is possible that WTP may be higher for a programme focusing more on these aspects and clearly communicating this to potential participants.

5.3. Limitations of Our Study

Although we believe that this exploratory study offers insights into patients’ WTP for nature-based therapies in Italy and highlights important features and potentials, we should acknowledge the presence of several limitations, including the limited sample size, representativeness of the sample, unbalanced bid design and strong beliefs that the State should pay.

Considering our sample size of 98 respondents, we recognise the potential limitations in the precision of these estimates. Our relatively small sample size is due to the specific target group, i.e., individuals suffering from or at risk of cardiovascular disease, who represent approximately 13 percent of the total population in Italy [72]. Moreover, despite the questionnaire being anonymous and obtaining ethical clearance, individuals may have been apprehensive in answering a questionnaire on a sensitive topic such as health, potentially explaining our relatively low response rate of 26%. In addition, it is worth noting that 2% of respondents were not confident in their answers to the WTP questions. Having a larger sample size would allow for more robust analysis and hence more certainty regarding the influencing factors and WTP estimates. Nonetheless, the sample size is comparable to other studies focusing on preferences and WTP for cardiovascular and pulmonary rehabilitation [70,73]. Despite limitations, we believe that these preliminary observations can provide indications of possible economic values of a thus-far-understudied but promising field of application of nature-based therapies.

Additionally, due to the randomisation process used, our study does not have the recommended equal number of responses for each initial bid value [74]. The LimeSurvey platform’s predetermined algorithm, while ensuring randomness, inadvertently introduced this unbalance into our study design. However, in certain situations unbalanced designs may produce reliable estimates [75]. Therefore, while we acknowledge this as a potential issue, given the exploratory nature of our study, we believe that our WTP estimates still provide meaningful insights, though they should be interpreted with caution.

A final consideration is that the vast majority of respondents hold the belief that the costs of a nature-based therapy should be borne by governments or insurance agencies, and not patients themselves. This is likely to have a non-negligible effect on WTP answers and could suggest that our WTP estimates are understated.

5.4. Relevance for Policy and Management

Our results provide valuable insights into the potential integration of nature-based therapy into standard healthcare practices, as respondents of our specific target group (individuals with or at risk of a chronic lifestyle-related illness—cardiovascular disease) displayed a high interest in trying these approaches. If designed and offered with the control and support of professionally qualified guides and doctors, who can guarantee safe outdoor environments, these types of rehabilitation could offer alternatives to standard rehabilitation. Our findings indicate that those with a greater knowledge of NBTs may be more willing to pay for them. Despite not finding any significant relationship in our sample, the literature indicates that perceived benefits and threats are important factors influencing WTP [51]. Therefore, in order to increase the future adoption and acceptability of these approaches, clearly communicating information on NBTs, including the benefits and risks, to potential patients could be a worthwhile endeavour. This could reduce the pressure of an increasing demand for public health services at indoor clinical centres and potentially serve an increasing portion of the population expected to suffer from cardiovascular or other chronic non-communicable diseases in the future.

On the basis of our results, new decisions regarding the allocation or expansion of green and/or blue natural areas for health pursuits versus other uses can be undertaken in urban and peri-urban areas to create favourable conditions for nature-based interventions. Consequently, expanding or adapting outdoor natural spaces for specific target groups could improve the overall health of the general population in these areas. This is supported by research showing that increased green space near residential areas is associated with better perceived health outcomes [76]. Moreover, increased contact with nature could promote pro-environmental behaviours [7] and thus lead to increased nature awareness and protection. This could shift perspectives in a way in which natural areas are considered as spaces providing vital health benefits and not only areas for recreational activities, leading to more sustainable management practices. However, we have not specifically investigated outdoor nature-based rehabilitation and its effects on pro-environmental behaviour; thus, this remains an issue for further exploration.

Our results indicate significant interest in NBT, and given the increasing demand for health tourism [16], this is likely to impact traditional land-use activities. This emphasises the importance for decision makers to integrate health considerations into environmental management strategies and vice versa. According to our findings, NBT programmes need not be located in isolated and remote areas. As closeness and safety are highly appreciated, urban and peri-urban parks could therefore be suitable locations for interventions targeting people with specific health conditions who may require safe environments and, if necessary, quick and easy access to medical assistance.

Both urban and environmental planners, working synergically with doctors and managers of rehabilitation programmes, may want to consider this and, in addition, where possible, prioritise accessible areas with trees and diverse plant life. Clearly, there is a large potential for nature-based therapies targeting vulnerable groups (such as people at risk of cardiovascular diseases) in or in the proximity of urban areas, where lifestyle-related chronic diseases are on the rise [1].

From a healthcare perspective, this study demonstrates the added value from a patient perspective of incorporating nature-based solutions into the therapeutic process. These findings could encourage policy makers to promote such innovations, given that patients appear open to these approaches. Furthermore, the monetisation of the health benefits from natural spaces could be an effective way to shift public health policy towards a more nature-based approach, where the current system is dominated by a focus on medical intervention [16] and at the same time the costs of public health are growing [6]. Monetary valuation is an important tool to quantify intangible outcomes of nature-based therapies in terms of improved health. Translating these benefits into economic terms, such as those provided in this study, offers policy makers compelling information in the same language as investment decisions, where nature’s benefits are often underrepresented [24].

The monetary value for a nature-based therapy, estimated as individuals’ willingness to pay per day, ranges from EUR 14.01 to EUR 42.69 per day (95% CI), with a median of EUR 27.26. Although this value should be considered with caution given the exploratory nature of our study, it represents a substantial added value from a patient perspective of the nature-based programme beyond the clinic-based option. Therefore, it can stimulate policy makers in funding pilot initiatives. It is necessary that decision makers are provided with reliable and comprehensive evaluations in order to guide effective and sustainable integration and roll-out beyond research contexts [65]. This would be useful not only to justify investments in innovative nature-based therapy but also to guide their implementation in both healthcare and environmental management strategies. Nature-based therapies are not yet widely implemented in health systems or markets in Italy and, more generally, in Europe, rendering it difficult to determine their value through conventional market prices. Therefore, the non-market valuation techniques we applied in this study offer a viable alternative for estimating the potential economic benefits of these interventions and guiding innovations in this field. To conclude, it is important to highlight that our study has estimated the value of benefits from a patient perspective, thus adopting a distinctly anthropocentric approach. Although this is beyond the scope of this study, we also invite researchers to consider in the future the impacts of nature-based therapies on natural spaces themselves. Externalities from the integration of outdoor nature-based therapies in health systems are likely to occur both for natural environments and public expenses, and further research on these key aspects is needed.

6. Conclusions

Interest is growing in nature-based therapy as a novel approach with the potential to alleviate some of the health issues associated with modern living. This study addresses key knowledge gaps related to this emerging field by investigating the economic value of a nature-based rehabilitation programme. This programme targets patients with cardiovascular diseases—one of the leading causes of death worldwide and a primary contributor to the economic burden of disease in many countries. Using a sample of respondents in Italy, we found a significant willingness to pay for an innovative outdoor nature-based rehabilitation programme with respect to a conventional indoor clinical-based programme. The estimates range from EUR 14.01 to EUR 42.69 per day (median value EUR 27.26). We found that the willingness to pay is influenced by, among other factors, the level of knowledge on nature-based therapies. Therefore, policies and programmes aimed at increasing public knowledge and awareness of this topic could help enhance willingness to pay and inform funding prioritisation. Furthermore, our findings on attitudes towards the features and benefits of nature-based therapy highlight simple yet relevant aspects to prioritise, especially in urban and peri-urban contexts.

These insights can inform sustainable health policies, green area management and land planning strategies, creating potential synergies that support long-term environmental and social wellbeing. In this way, our study aims to bridge disciplines and stimulate cross-sector debate on nature’s therapeutic potential, addressing the need for a more integrated approach that acknowledges diverse values and attitudes and the interconnectedness of human and environmental health. Our findings provide information that encourage collaboration between public health authorities and natural area managers—a recommendation that the European Environment Agency has promoted for over a decade [26].