A Bibliometric Review of Indoor Environment Quality Research and Its Effects on Occupant Productivity (2011–2023)

Abstract

Over the past decade, there has been a growing recognition of the importance of indoor environmental quality (IEQ) in influencing occupant productivity. Researchers have studied various buildings, including offices, schools, hospitals, and residential settings, to understand the relationship between IEQ and productivity outcomes. Studies have taken a multifactorial approach, considering multiple aspects of IEQ. Evidence from the literature review suggests that the quality of the indoor environment is an essential factor that affects the productivity of building occupants, and it is one of the fundamental issues in the development of societies. This area of research requires the responsible participation of researchers at all levels, as there is significant scope to contribute to knowledge. Therefore, this study aims to conduct a bibliometric analysis of the published literature on indoor environmental quality and its impact on building occupant productivity through the scientific literature available from one of the largest and most famous academic databases, Scopus; the study was determined in 2011 to 2023. The search used differential thresholds for IEQ keywords affecting building occupant productivity. Three discrete queries were performed, resulting in approximately 3861 publications. These were filtered by reducing false positives and excluding publications irrelevant to the research topic. The final results were 72 publications. This study also used Excel and VOS viewer to analyse and create graphs and network visualisation maps to show the growth of publications and their types, active countries and institutions for recovered publications, international collaboration, author keywords, active journals, and citation analysis. This study can significantly advance our understanding of building occupant productivity and enhance quality of life and work. Evaluating the research outputs is essential for highlighting contributions to knowledge and global collaboration in this research area. The potential impact of this study is not just theoretical. It can shape the future of our built environments and the lives of those occupying them.

1. Introduction

Modern societies use buildings to protect occupants and enhance their scientific and practical activities in various indoor environments. Studies indicate that the time spent by occupants of these buildings indoors is about 80% of their time, a statistic that underscores the significant impact of the indoor environment on their health and productivity [1,2]. This high percentage of indoor time highlights the indoor environment’s crucial role in shaping individuals’ overall well-being and productivity. The indoor environment can have both positive and negative effects on occupants. A positive indoor environment can reduce the risk of illness, decrease absenteeism, and improve concentration and productivity. Conversely, a hostile indoor environment can increase the risk of illness, raise absenteeism, and reduce concentration and productivity. Poor indoor air quality, elevated carbon dioxide levels, and extreme indoor temperatures can all contribute to adverse health effects [3,4,5].

The academic literature suggests that good IEQ improves building occupants’ satisfaction, health, and well-being. However, the research studies on improving performance and productivity in indoor spaces, to which the audience actively contributes, should be represented more in the literature. The audience’s contributions are not just invaluable, they are integral and have significantly shaped the field. Their work is not just a part of the literature, it is a driving force behind it. Productivity is a complex concept used in various fields to assess intellectual and practical activity, further complicating the principles of production efficiency. However, it is generally accepted as the output per unit of input used in production. The unit of input may be a unit of time. Therefore, the output unit is quantitative; where the output increases during the same period, the productivity of the process is said to increase. The literature suggests that occupants’ performance and productivity are affected by several factors: environmental, design, physiological, and technical factors [6,7,8]. The peer-reviewed literature that investigated the factors affecting the productivity of building occupants from 2011 to 2023 indicated that indoor environmental factors attracted the most significant interest from the researchers, including the audience. This was reflected in the 352 peer-reviewed publications during this period, a testament to the audience’s invaluable and integral contributions. This accounts for approximately 90.5% of the total number of publications. The preponderance of evidence in the literature suggests significant positive correlations between the productivity of building occupants and the IEQ factors [8,9,10].

Herzberg (1966) and Heschong (1979) were among the first researchers to shed light on the indoor environment’s impact on occupant productivity [11]. Their work has paved the way for the current study and inspired further research. Indoor environmental quality (IEQ) consists of conditions within a building, such as indoor air quality (IAQ), thermal comfort (TC), acoustic comfort (AC), visual comfort (VC), and ergonomics, and their effects on the occupants or residents. Some research shows that improving indoor environment quality reduces the causes of diseases, stress, absenteeism, and lack of focus [12,13,14]. Bibliometric analysis is the application of statistical methods to the published literature to explore and analyse large amounts of scientific data on a specific topic and shed light on the volume of research, researchers, countries, and institutions in this field [15]. Bibliometric analysis is a powerful tool for understanding research trends, hotspots, and gaps in various fields, including studies on indoor environment quality and occupants’ productivity. Using statistical methods, researchers can visualize and measure the evolution of the literature, thus guiding future inquiries. To date, no bibliometric study has been published on the impact of indoor environmental quality on building occupant productivity, and this study aims to address this gap. The proposed study, which will be the first to utilize Scopus, the most extensive database, as the primary source for studies focusing on the impact of indoor environmental quality on building occupant productivity from 2011 to 2023, is a collaborative effort that involves the collective expertise of academic researchers, architects, building operators, and the construction industry. This study aims to analyse the literature on the effect of indoor environmental quality on the productivity of building occupants. The volume of the literature on productivity is a good indicator of national and international efforts to enhance indoor environmental conditions to improve productivity. Moreover, enhancing indoor environmental quality is a shared responsibility of all these stakeholders. As highlighted in this study, this collective effort directly influences building occupants’ health, well-being, and productivity. A well-designed indoor environment can improve air quality, thermal comfort, lighting, and noise levels, crucial indicators of indoor environmental quality [16]. For instance, poor indoor air quality can lead to health issues such as allergies and stress, ultimately impacting productivity [17]. The design of a building has a significant impact on the health and well-being of its occupants, highlighting the crucial role of architects in incorporating sustainable practices that prioritize these factors. By concentrating on these aspects, building operators can establish environments that promote the physical health of building occupants and enhance cognitive function and overall productivity [18]. Therefore, a comprehensive assessment of indoor environmental quality is beneficial and essential for maximizing workplace effectiveness and ensuring long-term occupant satisfaction [16,19].

This study presents and analyses peer-reviewed published research on keyword analysis, number and types of published publications, research growth and key authors, research fields and response, leading journals, highly cited articles, and paper distribution metrics and research themes.

2. Method

2.1. Database Used

In this systematic search, the study developed a search strategy to identify the relevant studies on the impact of indoor environmental quality and occupant productivity. The study used the bibliometric methodology for quantitative and qualitative literature descriptions. The data used in this study were retrieved from one of the largest and most well-known academic literature databases, SCOPUS. It contains more than 27,950 active titles from more than 11,678 international publishers; approximately 34,643 of these publications are subject to peer review. Scopus covers various formats (books, journals, conference papers) in science, technology, medicine, social sciences, engineering, environmental sciences, arts, and humanities [20]. Also, studies have utilised SCOPUS data for various analyses, such as examining grey literature usage [21], conducting bibliometric analyses [22], identifying authors [23], and analysing extensive data publications in libraries [24].

2.2. Search Strategy

The comprehensive review resulted in a search in Scopus for “Indoor Environment Quality” OR “IEQ”; quotation marks were used to retrieve exact words. This query resulted in 2584 publications limited to journals in the subject area of engineering and environmental sciences. The search yielded 1677 publications. Differential thresholds for indoor environmental quality were used to exclude words that could lead to false positives. Publications were ranked by most cited. The top 50 publications were selected. A CSV file of the authors’ keywords was exported as an Excel file. The export resulted in 279 author keywords. The resulting keywords were filtered to ensure the study remained on track. Words unrelated to indoor environmental quality and duplicate words were excluded, resulting in 25 keywords that included the main factors and sub-factors of indoor environmental quality, which were classified into four groups: thermal comfort (air temperature, relative humidity, air velocity clothing, activity level, insulation); indoor air quality (air quality, air conditioning, ventilation, volatile organic compound); acoustic comfort (background noise, noise levels, acoustic environment, reverberation time); and visual comfort (lighting uniformity ratio, glare, visual ergonomics, natural light, artificial lighting, view privacy, illumination intensity). These words were used in search queries to limit all files published in this field. This process required significant effort and attention to detail, demonstrating our dedication and commitment to the research, and we are proud to present the results of our hard work, which we believe will significantly contribute to the understanding of indoor environmental quality.

The collective impact of thermal comfort, indoor air quality, acoustic comfort, and visual comfort on productivity is significant, often exceeding their individual effects. Research suggests that these indoor environmental quality factors interact in complex ways, impacting cognitive performance and overall comfort, essential for productivity. For instance, studies show that temperature is directly related to productivity measures such as office and factory output, with high and low temperatures leading to discomfort. This finding has practical implications for workplace design and management. It also mitigates the effects of noise and lighting on cognitive functions such as selective attention and creativity [25]. Indoor air quality is a critical factor that significantly impacts productivity and well-being. Poor air quality can lead to problems such as sick building syndrome, decreased cognitive function, and increased absenteeism, highlighting the need for a holistic approach to managing indoor air quality [26]. Acoustic comfort noise levels have been found to impact perceived comfort and cognitive performance, especially in open-plan offices [25]. Visual comfort also affects lighting conditions, including colour temperature, comfort, and mental performance, indicating a complex interrelationship between visual and thermal factors [25]. Therefore, addressing these factors collectively is essential to creating an ideal work environment.

The following tables show the extent of the impact of keywords on the number of retrieved publications from 2011 to 2023.

Table 1. Shows the number of publications resulting from the query on the main factors of indoor environmental quality from 2011 to 2023.

	Factors	The Year	Total	Grand Total
1	“Thermal comfort”	from 2011 to 2023	1094 publications	1752 publications
2	“Indoor air quality”	from 2011 to 2023	471 publications
3	“Visual comfort”	from 2011 to 2023	143 publications
4	“Acoustic comfort”	from 2011 to 2023	44 publications

shows a search query using keywords for the four main factors of indoor environmental quality shown in the table, and the total number of retrieved files was 1752 publications. Thermal comfort had the most significant number of retrieved publications, which reached 1094 publications, followed by indoor air quality with 471 publications, while auditory comfort had the least and received only 44 publications.

Table 2. The number of publications resulting from the query on the main and sub-factors of indoor environmental quality from 2011 to 2023.

	Factors	Sub-Factor	Year	Total	Grand Total
1	“Thermal comfort”	OR “Air temperature” OR “Atmospheric temperature” OR “Relative humidity” OR “Air velocity” OR “Clothing” OR “Insulation” OR “Activity level” OR “Energy utilisation” OR “Adaptive thermal comfort” OR “Thermal adaptation”.	From 2011 to 2023	21,470	188,060 publications
2	“Indoor Air Quality”	OR “Particulate Matter” OR “CO2” OR “carbon dioxide” OR “Concentration” OR “Air Quality” OR “Indoor Air Pollution” OR “Air Conditioning” OR “Ventilation” OR “Volatile organic” OR “VOCs” OR “formaldehyde” OR “Compounds” OR “Carbon Monoxide” OR “Mould” OR “Bacteria” OR “Volatile Organic Compounds” OR “Bad odour”.	from 2011 to 2023	111,368
3	“Acoustic comfort”	OR “background noise” OR “sound insulation” OR “noise levels” OR “acoustic noise” OR “speech intelligibility” OR “speech perception” OR “acoustic environment” OR “reverberation time “.	from 2011 to 2023	3129
4	“Visual comfort”	OR “illumination” OR “glare” OR “luminescence” OR “visual ergonomics “OR “natural light” OR “artificial lighting” OR “light” OR “View Privacy” OR “luminance”	from 2011 to 2023	52,093

shows keywords for indoor environmental quality’s four main factors and sub-factors. As shown in Table 2, the large number of publications is evident compared to Table 1, which reached 188,060 publications. Indoor environmental quality and its sub-factors received the largest share of the number of publications, which reached 111,368 publications, followed by thermal comfort and its sub-factors with 21,470 publications. This table shows the difference in results depending on the keywords used for each query.

Table 3. The number of publications resulting from the query on productivity from 2011 to 2023.

	Elements	The Year	Total
1	“productivity”	from 2011 to 2023	11,963 publications
2	“Occupants Productivity”	From 2011 to 203	4 publications

also shows the difference in the number of retrieved publications from 2011 to 2023 that use the keyword productivity or occupant productivity. Using generality as the productivity keyword produced 11,963 publications, while the query about specificity and occupant productivity produced 4 publications.

After obtaining the primary keywords, three sequential queries were conducted. The first query used the two primary search elements: indoor environmental quality (IEQ) and occupant productivity (PR). The second query added the selected four primary factors of indoor environmental quality: the productivity of building occupants. The third query used the keywords for the primary and secondary factors of indoor environmental quality and building occupant productivity. Quotation marks were used for each keyword in each query to retrieve exact words. The focus was on engineering and architecture, using the study period from 2011 to 2023, ensuring the relevance of our findings to current issues. English was chosen as the primary language of the search.

The researchers meticulously developed a ten-step process for this study. The first step involved using different sizes of keywords for every search query to retrieve the most significant possible number of publications related to the search. The number of publications retrieved from the three queries was approximately 3861. The second step was a rigorous filtering process, where the imported publications were carefully sifted to reduce false positive results and exclude publications irrelevant to the search by searching in the title and abstract. This process resulted in 116 publications. In the third step, duplicate publications were excluded in the second and third queries, bringing the number of excluded publications to 42. This filter resulted in 72 publications. Step four reinforced the effectiveness of the search strategy. The study collected data on the search outputs of each of the most active authors and reviewed their search outputs. The study observed a significant correlation between them. The fifth step reviewed the correlation coefficient between the various categories using IBM SPSS Statistics v26.

In the sixth step, the authors leveraged the comprehensive data provided by Scopus, including information about the authors of the publications, the number of citations, the countries active in the field, and the international cooperation between them. Step seven involved exporting the publications into Microsoft Excel. In the eighth step, the data were analysed, and several relevant publications to the research were identified, including the active scientific journals in the research area and the types of publications published.

The ninth step utilised the reliable VOS viewer software 1.6.17to prepare network visualisation maps of authors’ most popular keywords, author network visualisation maps and citation volume, and network visualisation maps of research collaborations between countries in the field. Step ten involved thoroughly analysing the resulting data, ensuring the validity and reliability of the study’s findings.

2.3. Bibliometric Analysis

The bibliometric analysis focuses on the quantitative and qualitative aspects of all publications retrieved from the Scopus database. Bibliometric analysis clarifies the volume of published research, how the volume of this literature has evolved, the scientific impact of the literature retrieved, the main topics that received significant attention during the study period, and the scientific influence of the literature on a specific topic.

The bibliometric analysis method was applied using one large and well-known Scopus database; a search was conducted of three inquiries on indoor environmental quality and occupant productivity. Validated, final retrieved files do not include duplicates, maps of bibliometric indicators were created for each query separately, and the study period was from 2011 to 2023. Search queries used differential boundaries for keywords. The researchers chose English as the research language. The researchers excluded any publications from other languages. Then, they defined the study area and restricted it to engineering and environmental sciences.

2.4. Data Analysis and Visualisation

This study used VOS viewer software to create a network visualisation map for research collaborations, a network visualisation map for the authors’ most popular keywords, a network visualisation map for international collaborations, and a network visualisation map of most cited authors. Hirsch’s index (h-index) was also used to measure the influence of publications. The graphs were created using the Excel program and then a data analysis was conducted for the most studied environmental factors, the types of buildings that were studied, the study methods used, the types of research gaps that were studied, and finally, the methods used to calculate the productivity of the occupants.

2.5. Query Analysis

The data used in the current study were retrieved from one of the largest and well-known academic literature databases, SCOPUS. A comprehensive query retrieved all publications related to indoor environmental quality and occupant productivity. The search query was uniquely developed to retrieve all publications for the current study. Furthermore, three inquiries were made using preferential keywords related to the quality of the indoor environment and the productivity of its occupants. The first step in the query analysis was to analyse the data exported from Scopus in Microsoft Excel. In addition to analysing the data in Microsoft Excel, three queries were used: obtaining the annual growth of publications, publishing sources, active authors, active countries, type of published publications, and authors keywords.

Search query validation: The first criterion for the query validation is to search all keywords related to indoor environment quality and their primary and sub-factors, then analyse each query’s results independently. Querying these words in Scopus reveals the results that appear from the search. The five most significant number of citations were chosen. The words related to the research subject were used in further searches. The second criterion was verifying the validity of the search queries and the relevance of the top five journals in AMS. Some journals, like Building and Environment, were returned in the three queries. However, Building and Environment published the most significant publications in the indoor environmental quality and occupant productivity field.

2.5.1. In the First Query

The first stage was conducting an advanced search in Scopus on indoor environment quality (IEQ) and occupants’ productivity only. Quotes were used to retrieve exact words. Using the words “Indoor environment quality” OR “IEQ” AND “Occupant’s productivity”, 31 publications resulted from this query from 2011 to 2023, as shown in Figure 1.

The keywords “Indoor Environmental Quality” or “IEQ” were returned, yielding 16 publications. “Occupant’s productivity” returned seven publications, while “productivity” produced 20. Figure 1 shows the growth in publications, it starts with two publications in 2012, followed by a period of volatility, then an increase to 6 publications in 2017, a sharp drop to 1 publication in 2018, a rise to 4 publications in 2021, and a decline and recovery to 4 publications in 2023, as shown in Figure 1. The publications retrieved from the first query were mainly research articles (20 publications, with a rate of 65%), review articles (5 publications, with a rate of 16%), and conference papers (5 publications, with a rate of 16%), as shown in Figure 2. The United Kingdom ranked first with eight publications at a rate of 26.66%. On the other hand, Brazil, Canada, Taiwan, and South Africa ranked last with one publication each at a rate of 3.33%, as shown in Figure 3.

For the funding Sponsor, the National Science Foundation was first with three publications. In contrast, the authors Mohammad Arif and Amit Kaushik topped the number of publications published in this query with 3 publications, as shown in

Table 4. Top 5 authors in the first query.

	Name of Author	NO Publications
1	Arif, M.	3
2	Kaushik, A.	3
3	Al Horr, Y	2
4	Elsarrag, E.	2
5	Mazroei, A.	2

. Youssef Al-Horr and others 2016 topped the list with the number of citations, reaching 506.

Table 5. Top 5 journals in the first query.

	Publication Sources	NO Publications
1	Building and Environment	8
2	Energy and Buildings	2
3	Proceedings of the 18th International Symposium on Advancement of Construction Management and Real Estate	1
4	Proceedings of the 9th International Windsor Conference 2016 Making Comfort Relevant	1
5	Journal Teknologi	1

shows the publication sources in the first query; Building and Environment topped the list with 8 publications, followed by Energy and Buildings with two papers, as showing in Table 5.

The analysis of the author’s keywords in the literature related to the first query indicated 98 author’s keywords. They were divided into ten groups. The word indoor environmental quality was repeated in four groups. In one group, indoor environmental quality ranked first and was repeated eight times; the total correlation strength was 39. Productivity was repeated eight times; the total correlation strength was 37. Occupant thermal comfort was repeated six times; the correlation strength was 31. Occupant productivity was repeated seven times; the total correlation strength was 30. Finally, indoor environmental quality was repeated five times; the correlation strength was 22, as shown in

Table 6. Top 5 author keywords extracted from the first query.

	Keyword	Occurrences	Total Link Strength
1	indoor environmental quality	8	39
2	productivity	8	37
3	thermal comfort	6	31
4	occupants’ productivity	7	30
5	indoor environmental quality(ieq)	5	22

and Figure 4.

The second stage was the filtering process, which involved looking at each document’s title, abstract, and keywords, selecting the publications that belong to the research, and excluding other publications. The 18 publications were the results of the first query, as shown in

Table 7. The publication results from the first query.

Number	1	2	3	4	5	6	7	8	9
Year	2016	2012	2014	2015	2015	2017	2017	2017	2017
References	[11]	[27]	[28]	[29]	[30]	[31]	[32]	[33]	[34]
Number	10	11	12	13	14	15	16	17	18
Year	2017	2018	2020	2021	2021	2023	2023	2023	2023
References	[10]	[35]	[36]	[37]	[38]	[39]	[40]	[41]	[42]

and Figure 5.

2.5.2. In the Second Query

The first stage was conducting an advanced search in Scopus on indoor environment quality (IEQ) and the main factors that affect the occupants’ productivity. Quotes were used to retrieve exact words, such as “indoor environmental quality” OR “thermal comfort” OR “visual comfort” OR “acoustic comfort” OR “indoor air quality” AND “Occupants’ Productivity”; 76 publications resulted from the query. The second query resulted in 76 publications from 2011 to 2023, as shown in Figure 6.

The keyword “productivity” returned 37 publications, “thermal comfort” returned 27 publications, and “indoor environmental quality” returned 27 publications. Figure 6 depicts the growth in publications, it commences with five publications in 2011, followed by a period of volatility. The trend then stabilizes with 7 publications in 2017, a brief decrease to 3 in 2018, and a significant rise to 12 publications in 2021, a point of particular interest. The trend then recovers, reaching 13 publications in 2023, as showing Figure 6. The publications retrieved from the second query were mainly research articles (43 publications, with a rate of 56%), conference papers (21 publications, with a rate of 28%), and review articles (9 publications, with a rate of 12%), as showing in Figure 7. The diagram for active countries in the second query shows that the United States ranked first with 19 publications with a percentage of 29.23%, while the United Kingdom had 14 publications with a share of 21.53%. In contrast, Canada and Denmark ranked last with two papers each, with a share of 3.07%%) As showing in Figure 8.

The National Science Foundation topped the list for the funding sponsor with six publications. In contrast, the author Mohammad Arif topped the list with the highest number of publications published in this query with four publications, as shown in

Table 8. Top 5 authors in the second query.

	Name of Author	NO Publications
1	Arif, M.	4
2	Becerik-Gerber, B.	3
3	Ben-David, T.	3
4	Kaushik, A.	3
5	Rackes, A	3

. Youssef Al-Horr and others 2016 topped the list with the highest number of citations, reaching 506.

Table 9. Top 5 journals in the second query.

	Publication Sources	NO Publications
1	Building and Environment	15
2	Energy And Buildings	9
3	Facilities	2
4	Journal of Building Engineering	2
5	Building	1

shows the publication sources in the Second query; Building and Environment topped the list with 15 publications, followed by Energy and Buildings with 9 publications, as showing in Table 9.

The analysis of the author’s keywords in the literature related to the second query indicated 233 author keywords. They were divided into 14 groups. The word indoor environmental quality was repeated in four groups. Again, thermal comfort was the most common, with 17 repeated occurrences; the total link strength was 75. Indoor environment quality had 14 occurrences, for a total link strength of 73. Productivity had 13 occurrences; the total link strength was 62. Occupant productivity had 9 occurrences, for a total link strength of 41. Finally, the Indoor air quality rate had 6 occurrences for a total link strength of 28, as shown in

Table 10. Top 5 author keywords extracted from the second query.

	Keyword	Occurrences	Total Link Strength
1	Thermal comfort	17	75
2	Indoor environmental quality	14	73
3	Productivity	13	62
4	Occupants’ productivity	9	41
5	Indoor air quality	6	28

and Figure 9.

The second stage was the filtering process. By looking at each document’s title, abstract, and keywords, the number decreased to 33 publications, with 16 duplicating the publications resulting from the first query. So, 17 publications were the results of the second query, as shown in

Table 11. The publication results from the second query.

Number	1	2	3	4	5	6	7	8	9
Year	2022	2013	2016	2017	2015	2019	2019	2020	2020
References	[8]	[43]	[32]	[44]	[45]	[46]	[47]	[48]	[49]
Number	10	11	12	13	14	15	16	17
Year	2021	2021	2021	2021	2022	2023	2022	2023
References	[50]	[51]	[42]	[52]	[53]	[54]	[55]	[56]

and Figure 10.

2.5.3. In the Third Query

The first stage was conducting an advanced search with the query on indoor environmental quality with the primary and sub-factors affecting the occupants’ general productivity. Quotes have been used to retrieve exact words, such as “Indoor Environment Quality” OR “Thermal comfort” OR “Air Temperature” OR “Relative Humidity” OR “Air Velocity” OR “Clothing” OR “Activity level” OR “Insulation” OR “Indoor Air Quality” OR “Air Quality” OR “Air Conditioning” OR “Ventilation” OR “volatile organic compound” OR “Acoustic Comfort” OR “Background Noise” OR “Noise Levels” OR “Acoustic environment” OR “Reverberation Time” OR “Visual comfort” OR “Lighting uniformity ratio” OR “Glare” OR “Visual Ergonomics” OR “Natural Light” OR “Artificial Lighting” OR “View Privacy” OR “illumination Intensity” AND “Productivity”. This query resulted in about 3754 publications in the first stage. For example, the keyword “productivity” was found in in 843 publications, “air temperature” in 572 publications, “Climate Change” in 518 publications, and “Air Quality” in 505 publications. The number of publications and citations showed a sharp increase in publications from 188 in 2016 to 514 in 2023, as shown in Figure 11.

The keyword “productivity” resulted in 620 publications”, and “Air Temperature” resulted in 411 publications. “Air Quality” resulted in 36 publications, while “Thermal Comfort” resulted in 234 publications. Figure 11 shows the growth in publications, it starts with 150 publications in 2011, The number of publications slight increase to 188 publications in 2016, after that, there was a change in the number of publications with a sharp increase, reaching 451 publications in 2023. Also, the retrieved publications from the third query were mainly research articles (2530 publications, with a rate of 68%), conference papers (815 publications, with a rate of 22%) and book chapters (180 publications, with a rate of 5%), as shown in Figure 12.

The diagram for active countries in the third query shows that China is in first place with 732 publications, with a percentage of 24.8%. The United States is in second place with 695 publications, with a percentage of 23.6%. On the other hand, Japan ranked last with 154 publications at a rate of 5.2%, as shown in Figure 13.

The National Natural Science Foundation of China topped the list of funding sponsors with 287 publications, and the National Science Foundation was in second place with 135 publications. The National Key Research and Development Program of China had 91 publications. In contrast, the author Tanabe, S.I., topped the list of the highest number of publications published in this query with twenty publications, as shown in

Table 12. Top 5 active authors in the third query.

	Name of Author	NO Publications
1	Tanabe, S.I.	20
2	Warnock, P.	15
3	Chen, J.	10
4	Nishihara, N.	10
5	Tsushima, S.	10

. Tsai, Hsinhan and others in 2016 topped the list with the highest number of citations, reaching 2712.

Table 13. Top 5 active journals in the third query.

	Publication Sources	NO Publications
1	Building and Environment	121
2	IOP Conference Series: Earth and Environmental Science	106
3	Science of The Total Environment	102
4	Act Horticulturae	88
5	Agricultural And Forest Meteorology	75

shows the publication sources in the first query; Building and Environment topped the list with 121 publications, followed by IOP Conference Series: Earth and Environmental Science with 106, as showing in Table 13.

The analysis of the author’s keywords in the literature related to the third query showed 10,190 author keywords. They were divided into 16 publication groups. The word thermal comfort was repeated in three groups. Productivity occupied the first place with 244 occurrences; the total link strength was 664. Thermal comfort had 238 occurrences; the total link strength was 509. climate change had 250 occurrences; the total link strength was 501. Finally, indoor air quality had 105 occurrences; the total link strength was 269. temperature had 82 occurrences; the total link strength was 204, as shown in

Table 14. Top 5 author keywords extracted from the third query.

	Keyword	Occurrences	Total Link Strength
1	Productivity	244	664
2	Thermal comfort	238	509
3	climate change	250	501
4	indoor air quality	105	269
5	temperature	82	204

and Figure 14.

The second stage involved filtering by looking at each paper’s title, abstract, and keywords. The number shrank to 185 publications; then, the publications were referenced and the introduction, the methods used, and the results were read; the query resulted in 65 publications, among which 15 publications were duplicated from the first query. A total of 13 publications were duplicated from the second query. So, 37 publications were the results of the third query, as shown in

Table 15. The publication results from the third query.

Number	1	2	3	4	5	6	7	8	9	10	11	12	13
Year	2022	2013	2016	2017	2015	2019	2019	2020	2020	2021	2021	2021	2021
References	[57]	[58]	[59]	[60]	[61]	[62]	[63]	[64]	[65]	[66]	[67]	[68]	[69]
Number	14	15	16	17	18	19	20	21	22	23	24	25
Year	2022	2023	2022	2023	2015	2018	2018	2018	2018	2021	2019	2019
References	[70]	[71]	[72]	[73]	[74]	[75]	[76]	[77]	[78]	[79]	[80]	[81]
Number	26	27	28	29	30	31	32	33	34	35	36	37
Year	2019	2019	2020	2020	2020	2020	2021	2021	2021	2021	2021	2023
References	[82]	[83]	[84]	[85]	[86]	[87]	[88]	[89]	[38]	[90]	[91]	[92]

and Figure 15.

The result from the first inquiry was 18 publications + 17 publications from the second inquiry + 37 publications from the third inquiry = a final total of 72 publications. Bibliometric indicators from the data retrieved for each query were exported to Microsoft Excel. The data exported included authors, titles, years, citations, funding agencies, countries, institutions, and journals. Then, the files were separately filtered and exported to the Excel file from the three queries. Finally, a line graph for the three queries was created to illustrate the annual growth of publications from 2011 to 2023.

3. Results

This analysis focused on a comprehensive review of 72 publications resulting from the three queries. Each document was meticulously investigated, its content analysed, and the resulting data were added to the Excel file. The added data were then analysed, revealing key insights such as the factors affecting occupant productivity, the types of buildings studied, the research methods used, the methodology employed, and the types of research gaps explored. This rigorous approach ensures the reliability and depth of our findings.

3.1. The Growth of Publication and Types

The search strategy yielded many publications, with 3861 publications from 2011 to 2023. After eliminating duplicates and applying filters, we focused on the 72 most relevant publications. The number of publications in this field has shown a fluctuating trend, with a peak of eleven publications in 2021, a dip to three publications in 2022, and a recovery to seven publications in 2023. Figure 16 shows the annual growth of the leaflets. There was a 75% increase in publications in 2021 compared to 2011. This trend reflects the evolving interest in indoor environmental factors affecting occupants’ building productivity.

The sources were Building and Environment, which published fourteen publications, followed by Energy and Buildings, which published five publications. Facilities and The 10th International Conference on Healthy Buildings 2012 each published three publications. Two publications were published in the Journal of Healthy Buildings in Europe 2015, HB 2015—Conference Proceedings. The analysis of publication types showed that research articles (forty-three publications; 60%) were the most popular, followed by papers from conferences (twenty publications; 28%), and reviews (five publications; 7%), as shown in Figure 17. English was the primary language used in the publications. The fields subject to the publications are engineering sciences and environmental sciences. (Figure 18). The publishers were Elsevier Ltd. in the lead with 12 publications and a rate of 16.6%. The Eighth International Conference on Environmental Engineering ICEE 2011 published three publications at a rate of 4.16%.

3.2. Active Countries and Institutions for Recovered Publications

Researchers from 38 different countries contributed 72 publications retrieved from the three inquiries.

Table 16. The table shows the types of publications generated by the three queries.

	Type of Publications	Publications	Percentage	References
1	Article	43	60%	[27,30,31,32,33,34,35,36,37,39,41,42,45,46,48,49,50,51,52,53,55,56,62,65,68,70,72,74,75,76,79,81,82,84,85,87,88,89,90,92,93]
2	Conference	20	28%	[9,28,38,43,47,54,57,58,59,61,64,66,67,69,73,78,81,86,94,95]
3	Review	5	7%	[9,11,45,83,96]
4	Book Chapter	3	4%	[60,63,91]
5	Short Survey	1	1%	[77]

lists the top five countries actively researching indoor environmental quality and occupant productivity. Researchers from the United States of America and The UK participated in publishing 12 publications (12.37%) each. The top five list included Japan, China, Australia, Italy, Malaysia, Switzerland, Denmark, and New Zealand. Researchers from these countries participated in publishing 60 publications (61.85%). Figure 19 shows a geographical distribution map of research published about indoor environmental quality and occupant productivity research extracted from the three inquiries (2011–2023). The regional distribution of the retrieved publications indicated that North America, Europe, and Asia had the highest contribution. At the same time, South and Central Africa made a minor contribution, as shown in Figure 19.

3.3. International Collaboration

3.3.1. Between Countries

Five groups were involved in international cooperation research, a significant endeavour, concerning the association between improving building occupants’ productivity and improving the indoor environment’s quality. There was relatively adequate cooperation between countries within each group and sufficient collaboration between the US and UK for two different groups (Figure 20). The first group consisted of eleven countries, a mixture of Asian countries associated with European countries and the USA (United States, China, Denmark, Greece, Indonesia, Japan, Latvia, Lithuania, Singapore, Turkey and the United Arab Emirates) shown in red. In contrast, the second group consisted of three countries in different regions (the United Kingdom, Qatar, and India), shown in purple. The third group comprised ten countries (Australia, Germany, Ghana, Hong Kong, Iran, Lebanon, Malaysia, New Zealand, South Africa, and Sri Lanka) shown in green. The fourth group was blue, consisting of five countries, most notably (Italy, Brazil, Netherlands, Poland, and Taiwan). The fifth group is yellow, consisting of three countries (Switzerland, Canada, and Slovenia). International cooperation has yet to emerge between countries in the Mediterranean region, Africa, or Eastern Europe and those in South America, as shown in

Table 17. Top 5 active international collaboration studies on the effect of indoor environment quality on the productivity of occupants extracted from the result of the three queries.

	Country	Publications	Citation	Total Link Strength	References
1	United States	12	172	1550	[35,45,46,52,56,63,75,83,88,91,94]
2	United Kingdom	12	433	1095	[9,11,27,31,36,37,42,48,49,53,78,92]
3	Japan	8	137	82	[47,61,67,69,72,73,80,90]
4	China	7	576	592	[33,56,57,59,62,64,93]
5	Australia	4	28	336	[30,44,82,87]

and Figure 20.

3.3.2. Between Institutions

International collaboration between institutions This research included the 153 most important institutions that supported research related to indoor environmental quality and passenger productivity (2011–2023) and were divided into eight groups. It appears that there is apparent cooperation between these institutions to work on the success of such studies, most notably Building Technology and the Department of Urban Systems, Lawrence Berkeley National Laboratory, United States, Center for Flexible Large-Scale Power Transmission (Current) Networks, Department of Electrical Engineering and Computer Science, University of Tennessee, US, Department of Civil and Environmental Engineering, University of Washington, US, Department of Construction Management, Louisiana State University, US, Engineering Department, University of Perugia, via g. Durante 91, Perugia, 06125, Italy, Department of Environmental Engineering (Qatar), University of Calabria, Italy, Energy Efficiency Group, Institute of Environmental Sciences and Forel Institute, University of Geneva, Switzerland, Center for Insight, National Taiwan University, Taiwan, Energy Efficiency Lab in Buildings, Federal University of Santa Catarina, Brazil, and Poznań University of Technology, Poland. The disclosure suggests that the towers of financiers are the departments of scientific universities, as shown in

Table 18. Top 5 active institutions support research about indoor environmental quality and occupants’ productivity (2011–2023).

	Name of Institutions	Publications	Citations	Total Link Strength
1	Building Technology and Urban Systems Division, Lawrence Berkeley National Laboratory, United States	1	25	1200
2	Center for Ultra-Wide-Area Resilient Electrical Energy Transmission Networks (curent), Department of Electrical Engineering and Computer Science, university of Tennessee, United States	1	25	1200
3	Department of Civil and Environmental Engineering, University of Washington, United States	1	25	1200
4	Department of Construction Management, Louisiana State University, United States	1	25	1200
5	Department of Engineering, University of Perugia, via g. Duranti 91, Perugia, 06125, Italy	1	25	1200

and Figure 21.

3.4. Author Keywords

Author Keywords The author keywords analysis showed 212 keywords divided into 28 groups. The most common keyword was (productivity) with 26 publications and a total correlation strength of 126. The keyword (thermal comfort) appeared in 13 publications and a total correlation strength of 56. Indoor environmental quality had nine occurrences and a total correlation strength of 42. Indoor environmental quality had seven occurrences and a total correlation strength of 38. Indoor environmental quality had six occurrences, with a total correlation strength of 26, as shown in Figure 22 and

Table 19. Top 5 author keywords extracted from the result of the three queries.

	Keyword	Occurrences	Total Link Strength
1	Productivity	26	126
2	Thermal comfort	13	56
3	Indoor environment quality	9	42
4	Indoor environment	7	38
5	Indoor environment quality(ieq)	6	26

.

3.5. Active Journals

The study showed that there were 63 active journals that participated in publishing retrieved publications on indoor environmental quality and building occupant productivity from 2011 to 2023. The most active journals were Building and Environment (fourteen publications, 22.2%), followed by Facilities, Building Engineering, Energy and Buildings, and The Tenth International Conference on Healthy Buildings 2012 (three publications, 4.76%). Construction Services, Engineering Research and Technology, and Health Buildings in Europe 2015, HB 2015—Conference Proceedings ranked third (three publications, 4.76%). These journals have made significant progress in this area, as shown in Figure 23 and

Table 20. Top 5 journals resulting from the three inquiries.

	Publication Sources (Journal)	Frequency	%
			N = 63
1	Building and Environment	14	22.2
2	Facilities	3	4.7
3	Journal of Building Engineering	2	4.7
4	Energy and Buildings	5	4.7
5	10th International Conference on Healthy Buildings 2012	3	4.7

.

The results show that the primary active journals from the final query are the same as those found in the previous three queries. Building and Environment had the most published publications, with 14.

3.6. Authors Publications and Citation Analysis

The results of the three queries have led us to 180 names of the most essential authors in research on indoor environmental quality and building occupant productivity. This identification of the most influential authors in the field is the result of a thorough and rigorous analysis. The third criterion for validating the queries was to search for the best active authors in each query and compare them with the results of the best authors in the final publication. After conducting a comprehensive analysis, we found that the names of some of them were repeated in the first and second queries. Tanebe, S. Arif, M., Kaushik, A., Zhu, Y., and Tsushima S. are among these influential authors, each with their unique impact on the field. Tanebe, S for instance, published four publications, with a citation rate of 128 and a correlation strength of 4.

In contrast, Arif, M. and Kaushik, A. each published three publications, with a citation rate of 376 citations and a correlation strength of 31. Zhu, y. published three publications, with a citation rate of 175 citations and a correlation strength of 47, while Tsushima, S. published three publications, with a citation rate of 57 and a correlation strength of 0.

Table 21. Top authors resulting from network visualisation map of authors published in the field from the three inquiries.

	Name of Author	Number of Publications	Citations	Total Link Strength
1	Tanebe s,-i,	4	128	4
2	Arif, M	3	376	31
3	Kaushik, A.	3	376	31
4	Zhu y,	3	175	47
5	Tsushima, S.	3	57	0
6	Al Horr, Y	2	342	27

and the network map in Figure 24 illustrate this.

This section presents the most cited publications, 72 of which were published. The author and year of publication are also shown. The most cited publication was Al-Horr (2016), with 326 citations and a correlation strength of 6, followed by Lan l; Wargocki p; lian Z. (2011), with 284 citations and no correlation strength, and Geng (2017), in third place, with 149 citations and a correlation strength of 7. These results are shown in

Table 22. The top 5 publication results from the network visualisation map of the most cited publications in the field.

	Publications	References	Citations	Links
1	(Al Horr et al., 2016)	[11]	326	6
2	Lan l; Wargocki p; lian z.(2011)	[57]	284	0
3	(Geng et al., 2017)	[93]	149	7
4	(Kang, Ou and Mak, 2017)	[33]	100	3
5	(Lipczynska, Schiavon and Graham, 2017)	[75]	78	7
6	(Mak and Lui, 2012)	[62]	71	2
7	(Tanabe, Haneda and Nishihara, 2015)	[72]	71	2

, and a network map in Figure 25, providing a visual guide to the distribution of citations and correlation strengths.

4. Discussion

4.1. Keyword Analysis

In this study, the authors reviewed the literature on indoor environmental quality and building occupant productivity by conducting an open search query in Scopus to extract the most commonly used keywords in research on this topic. This query resulted in 5687 publications arranged according to the most cited. The 50 most cited publications were selected.

From these publications, 273 keywords were collected. All keywords were collected in an Excel file. In the first stage, keywords that were irrelevant to the research topic and did not belong to the research about the quality of the indoor environment were excluded, resulting in 53 final publications. In the second stage, duplicate words were excluded, resulting in 25 keywords that were classified into four groups:

1—Thermal comfort (air temperature, relative humidity, air velocity clothing, activity level, insulation);

2—Indoor air quality (air quality, air conditioning, ventilation, volatile organic compound);

3—Acoustic comfort (background noise, noise levels, acoustic environment, reverberation time);

4—Visual comfort (lighting uniformity ratio, glare, visual ergonomics, natural light, artificial lighting, view privacy, illumination intensity).

These words were used in search queries to limit all files published in this field.

4.2. Growth of Publications Analysis

In this study, we analysed the outputs of global research on indoor environmental quality and its impact on the productivity of occupants from 2011 to 2023. The results of the publications obtained after the filtering process for the three queries showed 72 publications. The contribution of researchers from various scientific fields has accelerated the growth of publications in this field. The growth of publications showed a fluctuating state, with a sharp increase in the number of publications in 2023 with 12 publications, i.e., a 66% increase in the number of publications in 2023 compared to 2020. The study “Occupant Productivity and Indoor Office Environment Quality: (A Review of the Literature)” in 2016 garnered a large number of citations, reaching 326.

4.3. Active Countries and Institutions Analysis

Our results from the three inquiries showed that the United States and the United Kingdom have the highest research productivity for the current study. The United States has 12 publications, an average of 172 citations, and a correlation strength of 1550. The United Kingdom has 12 publications, an average of 433 citations, and a correlation strength of 1095. Also, it was found that some publications were under study for more than one country, such as a case study in Japan, India, Singapore, China, and Malaysia conducted by Yingdong He and others (2019) [45]. Also, the study conducted by Chen, Chien-Fei, and others (2020) was a case study in Brazil, Italy, Poland, Switzerland, and Taiwan [35].

From the analysis of the data generated by the VOS Viewer, it becomes clear that the United States and the United Kingdom ranked first with 12 publications (16.7%). Japan ranked second with eight publications (11.1%). China ranked third with seven publications (9.7%). Australia, Italy, and Malaysia ranked fourth with four publications (5.6%). Finally, Switzerland, Denmark, and New Zealand ranked fifth with three publications (4.2%). The presence of active institutions and many high-impact journals in the field of scientific research on the quality of the indoor environment and the productivity of the occupants contributed to improving the quality of the indoor environment, reducing absenteeism and the causes of sick buildings, and improving the productivity of the occupants. Supporters of these studies include the Alfred P. Sloan Foundation, Ecophene Saint-Gobain et al., Interface, TNO, Velux, as well as the American Concrete Institute (ACI), American Society of Civil Engineers (ASCE), Architectural Institute of Japan (AIJ), the Chartered Institute of Building (CIOB), Engineers Without Borders USA, and University of Hawaii at Manoa.

4.4. International Collaboration Analysis

The quality of the indoor environment and the productivity of its occupants are among the essential topics that received significant attention from some countries during the study period from 2011 to 2023. The extent of international cooperation in the research was relatively low, with the United States being the most internationally cooperative, with a total link strength of one thousand five hundred and fifty in the number of publications, which reached 12. The United Kingdom had the same number of publications, but the total strength of the association reached one thousand ninety-five. Likewise, Japan had eight publications, but the strength of the association was weak, reaching Eighty-two. In contrast, China had fewer publications than Japan (seven publications), but the strength of the association was greater. China came in fourth, as did Australia, which had only four publications but an overall link strength of Three hundred and thirty-six. On the other hand, Slovakia, Egypt and Czech Republic had the lowest link in international cooperation, with a link strength of zero and one publication. It has become clear that the number of publications or citations does not measure the strength of the connection between countries.

4.5. Highly Cited Publications Analysis

The most frequently cited d publications in this area were related to occupant productivity and the quality of the indoor office environment: a literature review received many citations, which suggests great importance, as the number of citations reached 326. Publications concerning the effect of the thermal environment on the perception and productivity of occupants reached 149 citations, and publications concerning the effect of the quality of the indoor environment on work productivity in open university research offices reached 100 citations.

5. Strengths and Limitations

This study concerned research activity in the field of indoor environmental quality and occupants’ productivity. Our study documented a significant increase in publications and the role of international collaboration. However, our study has several limitations. The Scopus database is a comprehensive and extensive database that includes different disciplines. Still, it is continuously growing, so the officials working on the database are constantly adding new data every day, and some peer-reviewed journals still need to be indexed in Scopus. This is especially true for journals published in India, Indonesia, other Asian countries, African countries, and South American countries where concern for the indoor environment’s quality and the occupants’ productivity is a significant problem and is not given much attention. Therefore, publications published in non-indexed journals were not retrieved. Secondly, the results obtained from the three inquiries in this study reflect the research strategy implemented, and it is comprehensive in relation to the research about the quality of the indoor environment, its main and subsidiary factors, and the productivity of the occupants. The authors found that there were false positives and negative results and some duplicate results; they worked to exclude and filter them all. In most bibliometric studies, it is noteworthy that one query method may only be comprehensive for all publications. Third, when listing the active authors and institutions, the authors relied on the score obtained from Scopus. However, some authors may have more than one Scopus profile, or their names may be typed in different articles differently, affecting their research output and, thus, their ranking. The same applies to active institutions whose names can be written in other articles, affecting their research output and order.

Moreover, the authors used the keyword “occupant productivity” in the search strategy in a strict manner to avoid false positive results, as the scope of the current study, which only focused on the relationship between indoor environmental quality and productivity, could not operate extensively. Finally, it should be made clear that the list of highly cited articles does not mean they are the only ones influential in the field. The citation process is dynamic; sometimes, the high citation rate reflects the author rather than the influence of the research, and the number of sources is variable and not fixed. Review studies were not cited, although some were reviewed before the study period. The study included various types of publications and did not exclude any kind. The filtering process for the files led to the desired accurate results.

6. Conclusions

Our bibliometric study, the first of its kind, examines how to improve indoor environmental quality and occupant productivity. The current study highlighted that integrating multiple dimensions of indoor environmental quality (IEQ) significantly influences occupant productivity. Thermal comfort, indoor air quality, acoustic comfort, and visual comfort collectively impact productivity. The comprehensive assessment provides critical insights into the complex interplay between IEQ factors and their combined effects on human performance. It offers valuable perspectives for researchers and policymakers aiming to improve work environments. The study provides a unique perspective on the global landscape of IEQ research, highlighting key contributors, collaborative networks, and emerging research directions. It also underscores the importance of comprehensive IEQ strategies in building design and management, which can significantly improve occupant productivity and overall well-being. The need for further work to explore the specific mechanisms through which these IEQ factors interact to impact productivity is a compelling area for future research. Also, investigating innovative technologies, such as intelligent building systems, and exploring under-researched regions could provide a more comprehensive understanding of global IEQ challenges and opportunities, providing a unique and comprehensive perspective. The current study provides researchers and policymakers with critical data in this area. It emphasises the importance of improving occupant productivity and its necessity to develop communities and reduce energy consumption. When productivity increases, income and production improve, and life improves, giving a positive impression that helps accelerate the individual’s and society’s development. Such topics encourage cooperation between producing companies and offices to enhance the productivity of their occupants and increase research cooperation between them because the returns will benefit everyone. Moreover, the field can move toward more effective solutions to improve indoor environments and support community development, fostering a sense of inclusion and shared purpose among all stakeholders.

7. Results

The most significant number of recovered publications on indoor environment quality and occupant productivity occurred in 2021; during this year, there were 11 publications. As for the publishing sources, Al-Bild and Environment obtained the highest rate, publishing 14 publications. The most influential authors of the inquiries are Arif, M., Koushik, A. and Tanebe, S. The United States and the United Kingdom have the highest percentage of countries active in this field, with 12 studies documented. The type of published file that had the highest rate was research articles, reaching 43 publications. Also, the author extracted the most important keywords from the queries: productivity and thermal comfort. The results from the second phase of analyses showed that the most critical factors affecting occupant productivity, which were then studied, were thermal comfort, with the highest rate, which reached 54 publications, and indoor air quality, with 48 publications.