Global Incidence of Attention Deficit/Hyperactivity Disorder among Children ^†

Abstract

In this descriptive epidemiological study, age-specific rates for attention-deficit and hyperactivity disorder (ADHD) incidence among children (0–14 years) were presented (per 100,000). Joinpoint regression analysis was applied to calculate the average annual percent change (AAPC) with the corresponding 95% confidence interval (CI) to evaluate trends in 1990–2019. Global ADHD incidence was nearly threefold that of girls (307.9 and 114.4 per 100,000, respectively) in 2019. Trends for global ADHD incidence were significantly decreasing both in boys (AAPC = −0.4%, 95% CI = −0.4 to −0.3) and girls (AAPC = −0.4%, 95% CI = −0.5 to −0.3).

1. Introduction

Attention-deficit/hyperactivity disorder (ADHD) is a chronic condition which involves a developmentally inadequate inattention level, hyperactivity, and/or impulsivity [1]. ADHD is among the most common childhood neurobehavioral disorders, persisting in a number of cases into adulthood [2,3,4]. A previous meta-regression analysis estimated that ADHD affects about 6% of children around the world, with a range from 1% to nearly 20% in school age children [2]. The significant differences in ADHD prevalence were described by geographic areas [2,5,6].

There have been only several studies reporting estimates of ADHD incidence trends, mostly indicating increasing incidence over the observed period [7,8]. However, some studies did not find an increase in ADHD incidence trends over the past years [5]. This study aimed to estimate the global incidence of attention-deficit and hyperactivity disorder among children in the last three decades.

2. Materials and Methods

2.1. Study Design

An observational descriptive epidemiological study was conducted to describe worldwide trends in the incidence of ADHD in the period 1990–2019.

2.2. Data Source

Data of ADHD incidence in children were obtained from the Global Burden of Disease Study 2019 [9]. In this study, age-specific rates of incidence for ADHD in children (0–14 years) were presented (per 100,000). Additionally, the socio-development level was quantified by the socio-demographic index (SDI), a composite measure comprised of income per capita, educational level for persons aged 15 years and older, and total fertility rate for women <25 years of age [9]. An SDI of 0 describes a theoretical minimum level of development as it pertains to health, while an SDI of 1 marks maximum level. Countries were divided into 5 SDI quintiles: low-, low–middle-, middle-, high–middle- and high-SDI countries.

2.3. Statistical Analysis

Joinpoint regression analysis was applied to determine the average annual percentage change (AAPC) with a 95% confidence interval (CI) to evaluate trends in 1990–2019 [10]. Additionally, disparities in trends of incidence by sex were assessed with a comparability test (specifically: test of parallelism) in order to determine if the two regression mean functions were parallel. A p value lower than 0.05 indicated statistical significance for all tests.

3. Results

Globally, there were 4,198,974 new ADHD cases in children (0–14 years) in 2019: it was diagnosed in 3,114,614 (74%) boys and 1,084,360 (26%) girls (Figure 1).

Global rate of ADHD incidence in boys was nearly threefold that in girls (307.9 per 100,000 and 114.4 per 100,000, respectively) in 2019 (Figure 2 and Figure 3). Globally, ADHD was a disorder that predominantly affected boys with a boy/girl sex ratio of approximately 3:1. Significantly decreasing trends for global ADHD incidence were observed both in boys (by −0.4% annually, 95% CI = −0.4 to −0.3) and girls (by −0.4% annually, 95% CI = −0.5 to −0.3) (Figure 2 and Figure 4). The trends of ADHD incidence in children in both sexes followed an oscillating nonlinear pattern, with a significant increase at the beginning of the observed period, and a continuously significant decrease in trends after 1995 in boys and after 1994 in girls. Based on the comparability test, global trends in incidence of ADHD in boys and girls were not parallel (final selected model rejected parallelism, p < 0.05).

In assessments of both sexes together, the highest ADHD incidence was observed in high-SDI countries (Figure 3). The incidence rates of ADHD in children across all SDI quintiles showed that boys experienced a higher disease burden compared with girls in 2019 (Figure 3). In boys, the highest incidence rate for ADHD in children was found in the high-SDI countries (521.28 per 100,000), followed by high–middle SDI countries (433.39 per 100,000), while the highest rates in girls were equally in high- and high–middle SDI countries (about 165.00 per 100,000).

Over the 1990–2019 period, a significant decrease in ADHD incidence rates in boys was noted in only one area—in middle-SDI countries (by −0.3% per year) (Figure 4). Contrary to that, the incidence rates of ADHD in boys significantly increased in high-SDI countries (by +0.2% per year), and low–middle- and low-SDI countries (equally by +0.1% per year). A significant increase in incidence of ADHD was registered in girls in high- and low–middle SDI countries (by +0.3% and +0.2% per year, respectively). In middle- and high–middle SDI countries a significant decrease was recorded (by −0.2% and −0.1% per year, respectively). Based on the comparability test, trends in incidence of ADHD by each SDI in boys and girls were not parallel (final selected model rejected parallelism, p < 0.05).

4. Discussion

The incidence of ADHD in children is still not well researched. Although not numerous, epidemiological studies on the ADHD incidence have shown increasing temporal trends of this disorder in some countries [3,8].

According to the available literature, until now there was no data on the global incidence of ADHD in children. Our study showed a decreasing trend in ADHD incidence among children in both sexes, with marked differences in trends by SDI. In contrast to the global trend, a pronounced increasing trend was observed in high SDI countries. The results of our study regarding the ADHD incidence among children are consistent with some previous research carried out in Spain [5], Slovenia [3], Canada [11], the USA [12], Germany [13].

The observed differences in ADHD incidence temporal trends in children could mainly be due to the implementation of new diagnostic criteria (ICD-10, etc.) and the use of different case definitions, overdiagnosis/underdiagnosis in different health care systems, geographical and demographic factors, different observation periods, and differences in study methodology.

In conclusion, ADHD remains one of the most common neurodevelopmental disorders in children, although a decreasing global trend in incidence was observed. To explain the reasons for variations in ADHD incidence in children across the world, future analytical longitudinal studies are needed.