Eur J Pediatr (2007) 166:117–123

DOI 10.1007/s00431-006-0299-5

REVIEW

Variations in prevalence of attention deficit hyperactivity

disorder worldwide
Maria Skounti & Anastas Philalithis &
Emmanouil Galanakis

Received: 20 May 2006 / Accepted: 28 August 2006 / Published online: 11 October 2006
# Springer-Verlag 2006

Abstract Attention deficit hyperactivity disorder (ADHD) Introduction

is among the most common, intensely investigated, and yet
diagnostically controversial neurobehavioral conditions of Attention deficit hyperactivity disorder (ADHD) is a hetero-
childhood. The prevalence of ADHD has been reported geneous disorder of childhood onset characterized by inatten-
with great variations among different studies, ranging from tion, impulsivity and hyperactivity [2, 11]. The prevalence
2.2% to 17.8%. The aim of this review was to investigate and the chronicity of the disorder, coupled with its ability to
the variables that influence the prevalence of ADHD and to interfere with major domains of developmental relevance,
derive a best estimate for the prevalence of the disorder. We make ADHD a major public health condition [28].
reviewed all the 39 studies on ADHD prevalence appearing As is true with most developmental disorders, there is no
in the Pubmed and published since 1992. These studies definite test for ADHD, and both diagnosis and classification
indicate that ADHD is more common in boys than girls, in rely on description. This lack of definite diagnostic tools has
younger than older children and adolescents, in one-setting lead to great variations of ADHD prevalence [46], which has
rather than two-setting screening studies, in studies based been reported from 2.2% to 17.8% [1, 3, 6, 8, 10, 12–14,
on DSM-IV rather than DSM-III-R criteria. Additional 18–23, 25–27, 31–36, 39–42, 44, 45, 47–49, 51, 53, 54, 56–
factors that may well influence prevalence rates include 58]. The purpose of this review was to investigate the
source of information and assessment of clinical impair- parameters that influence the prevalence of ADHD and to
ment. In conclusion, our findings suggest that population derive the best estimate for the prevalence of the disorder.
characteristics, methodology features, ethnic and cultural
differences and diagnostic criteria involved in studies affect
the prevalence of ADHD. Standardized designs may lead to Methods
firm conclusions on the true prevalence of ADHD, the
estimation of which seems impossible to be achieved by We reviewed all available articles in the PubMed from 1992
reviewing the already existing literature. through 2006 by using the key words “ADHD, prevalence,
assessment, epidemiology” and by screening the reference
Keywords Attention deficit hyperactivity disorder . lists of the obtained studies to identify papers reporting on
Prevalence . DSM-IV . Population screening prevalence of ADHD (Table 1). Studies were then checked
to establish the population and the diagnostic criteria used.
M. Skounti : E. Galanakis (*)
Only studies using DSM-III-R and DSM-IV criteria and
Department of Paediatrics, University of Crete, sampling from the general population or from well-
POB 2208, Heraklion 71003, Greece specified non-referred population were reviewed. The
e-mail: egalanak@med.uoc.gr reported prevalence of ADHD was subsequently analyzed
in relationship to gender and age of children, source of
A. Philalithis
Department of Social Medicine, University of Crete, information, evaluation procedure, and definition of the
Heraklion, Greece disorder.
118 Eur J Pediatr (2007) 166:117–123

Results samples, male-to-female ratio ranged from 1:1 to 3:1 [3, 7,

8, 10, 12–14, 18–20, 23, 32, 41, 42, 44, 45, 49, 51, 54, 56].
Table 1 summarizes the results of all 39 studies since 1992 Among children referred for clinical evaluation, the boy-to-
which matched to the study criteria. As clearly shown, the girl ratio increased to values up to 9:1 [4, 16].
prevalence of ADHD presented with considerable varia-
tions with reported rates varying among school-aged Age The influence of age on prevalence of ADHD was
children and adolescents from 2.2–17.8%. strongly supported by the findings of several studies. In the
study of Cohen et al. [12] a clear decline in prevalence was
Gender Both community and clinical samples clearly confirmed as age advanced. This study evaluated the
suggested higher ADHD prevalence in boys. In community frequency of psychiatric disorders in the same cohort of

Table 1 ADHD prevalence in 39 studies world-wide, 1992–2005

Country; year Children population Age in Informants Assessment tools Diagnostic ADHD Ref
years criteria pre-valence
%

2-settings studies
Sweden; 1996 N=589; community 6 Parent and teacher DSM-II-R scale DSM-III-R 4.0 (35)
Netherlands; N=853; community 13–18 Parent, adolescent, CBCL, TRF, YSR, DSM-III-R 2.6 (53)
1997 teacher, DISC, CGAS
England; 1999 N=10,438; community 11–15 Parent, child, teacher Interview DSM-IV 2.2 (20)
Australia; 1999 N=1,275; public schools 5–11 Parent and teacher DSM-IV scale, DSM-IV 2.4 (25)
Conner’s scale
Canada; 1999 N=2,400; community 6–14 Parent, child, teacher DISC DSM-III-R 3.3 to 8.9 (10)
Iceland; 1999 N=429; public schools 6–8 Parent and teacher ADHD scale DSM-IV 6.7 to 5.8 (36)
Sweden; 2001 N=429; public schools 7 Parent, child, teacher DSM-III-R scale, DSM-III-R 3.7 (33)
interview, clinical
USA; 2001 N=362; public schools 7–11 Parent and teacher DSM-IV scale DSM-IV 16.1 (45)
Colombia; N=330; community 4–17 Parent and teacher DSM-IV scale, DSM-IV 11.3 (42)
2003 interview
Greece; 2005 N=1,708; public schools 7 Parent and teacher ADHDT-Gilliam, DSM-IV 6.5 (49)
DSM-IV scale
Single-setting studies
Israel; 1992 N=562; military 16–17 Adolescent DSM-III-R, interview DSM-III-R 3.9 (58)
USA; 1992 N=931; national sample 5–14 Teacher Disruptive behaviour DSM-III-R 7.1 (41)
rating scale
USA; 1992 N=541; community 10–20 Parent and child DISC DSM-III-R 6.0 to12.8 (12)
Italy; 1993 N=232; public schools 8–10 Teacher DSM-III-R scale DSM-III-R 3.9 (21)
Taiwan; 1993 N=4,290; public schools 7–12 Teacher Conner’s scale DSM-III-R 9.9 (54)
N. Zealand; N=961; birth cohort 15 Parent and adolescent DSM-III-R scale DSM-III-R 2.8 to 3.0 (19)
1993
Spain; 1994 N=1,127; community 8, 11, 15 Parent and child CBCL K-SADS, DSM-III-R 14.4, 5.3, (26)
GAF scale 3.0
Japan; 1994 N=119; community 8 Parent and child CAS DSM-III-R 10.5 (51)
Japan; 1994 N=1,022; community 4–12 Parent Conner’s scale DSM-III-R 7.7 (34)
USA; 1995 N=1,285; community 9–17 Parent and child DISC, CGAS DSM-III-R 5.1 to 6.5 (47)
USA; 1995 N=294; military 6–17 Parent and child DISC, CBCL DSM-III-R 15.1 (32)
Germany; N=1,077; public schools 5–12 Teacher DSM-III-R scale DSM-III-R. 17.8 (6)
1995 DSM-IV scale DSM-IV 10.9
USA; 1996 N=8,258; public schools 5–12 Teacher DSM-III-R scale DSM-III-R, 7.3, (57)
DSM-IV scale DSM-IV 11.4
USA; 1996 N=1,420; community 9–13 Parent and child CAPA DSM-III-R 4.1 (13)
USA; 1997 N=2,762; white twins 8–16 Parent and child CAPA DSM-III-R 2.4 (48)
USA, 1997 N=2.744 Community K-5 Grade Teacher TRF DSM-IV 8.0 (22)
USA; 1998 N=1,269 pairs; females 13.5–19.5 Parent Interview DSM-IV 9.9 (31)
twins
Eur J Pediatr (2007) 166:117–123 119

Table 1 (continued)

Country; year Children population Age in Informants Assessment tools Diagnostic ADHD Ref
years criteria pre-valence
%

USA; 1998 N=4,323; public schools 5–12 Teacher DSM-IV scale DSM-IV 6.8 to 16.1 (56)
with impairment
Spain; 1999 N=387; community 10 Parent and child Interview, clinical DSM-III-R 8.0 (3)
assessment
Brazil; 1999 N=1,013; public schools 12–14 Parent and child DSM-IV scale, DSM-IV 5.8 (44)
clinical assessment
Finland; 1999 N=435; community 8–9 Parent Interview DSM-III-R 7.1 (1)
USA; 2000 N=253; daycare centers 2–6 Parent Rating scale DSM-IV 9.5 (23)
USA; 2001 N=3,006; schools 3–18 Teacher ECI-4, CSI-4, ASI-4 DSM-IV 15.8 (40)
Australia; 2001 N=3,597; national sample 6–17 Parent DISC DSM-IV 6.8 to 7.5 (27)
Venezuela; N=1,141; community 4–12 Teacher Conner’s scale DSM-IV 7.19 (39)
2002
Thailand; 2002 N=433; public schools 7–12 Parent Conner’s scale, DSM-IV 6.5 (8)
interview
Turkey; 2004 N=1,425; community 6–15 Parent or teacher DSM-IV scale DSM-IV 8.1 (18)
USA; 2005 N=10,367; community 4–17 Parent SDQ DSM-IV 6 (14)
Qatar, 2006 N=2,000; primary schools 6–12 Teacher Conner’s scale DSM-IV 9.4 (7)

ADHDT: Attention Deficit Hyperactivity Disorder Test; ASI-4: Adolescent Symptom Inventory-4; CAPA: Child and Adolescent Psychiatric
Assessment; CAS: Child Assessment Scale; CBCL: Child Behaviour Checklist; CGAS: Children Global Assessment Scale; CSI-4: Child
Symptom Inventory-4; DISC: Diagnostic Interview Schedule for Children; ECI-4: Early Childhood Inventory-4; GAF: Global Assessment
Functioning; SADS: Schedule for Affective Disorders and Schizophrenia; SDQ: Strengths and Difficulties Questionnaire; TRF: Teacher’s Report
Form; YSR: Youth Self Report

children during an 8-year follow-up. The prevalence of lower prevalence of ADHD compared with white children
ADHD was 12.8%, 9.0% and 6.0% for children-adolescents [20]. In the study of Cuff et al. (2005), hispanic children
aged 10–13, 14–16, and 17–20 years, respectively. In were significantly less likely to be diagnosed with ADHD
Spain, prevalence rates 14.4%, 5.3% and 3.0% were than their white peers. In this study, male ADHD
reported for three separate samples of children aged 8, 11 prevalence by race was 3.06% for hispanics, 4.33% for
and 15 years, respectively [26]. Similar findings were white and 5.6% for blacks.
reported in Canada, with prevalence rates of 5.5%, 4.0%,
and 2.5% for children aged 6–8, 9–11, and 12–14 years, Source of information ADHD prevalence seemed to vary
respectively [10], and in the USA, with prevalence rates depending on who was being asked to report symptoms
18.2%, 15.9% and 14.8% for children aged 3–5, 5–12 and [50]. Magnusson et al. reported ADHD prevalence in
12–18 years, respectively [40]. Icelandic schoolchildren at the level of 4.7% when parents
were asked, but 5.8% when teachers were asked [36].
Cultural and geographical differences in prevalence of Breton et al. demonstrated prevalence rates of 3.3%, 5.0%
ADHD Information on demographic distribution of ADHD and 8.9% when children, parents or teachers were asked,
is generally limited. Higher prevalence rates have been respectively [10]. Gomez et al. reported rates of 8.8% and
associated with lower socioeconomic status [23, 27, 33, 42, 9.9% when parents and teachers were asked, respectively.
51] and among urban as compared to rural residence [6], However, the prevalence rate dropped to 2.4% after
but no significant differences were observed regarding the diagnosis was based on both questionnaires [25].
place of residence in other studies [10, 14, 32, 40, 49].
Prevalence variations between different racial and ethnic One-setting and two-setting evaluation School-based stud-
groups have not been adequately examined. The study of ies commonly focused on a single setting (Table 1). Out of
Rowland et al. (2001) suggested little difference between the 39 studies, only 10 [10, 20, 25, 33, 35, 36, 42, 45, 49,
black and white children, and more racial differences in 53] were based on information from two settings and
medication treatment. Several studies have suggested reported prevalence rates from 2.2 to 16.1%. Four of these
higher prevalence rates in black than white children [15, studies [10, 33, 35, 53] used DSM-III-R criteria and the
17, 40, 43]. Ford et al. suggested that Asian children remaining six [20, 25, 36, 42, 45, 49] used DSM-IV
(Indian, Pakistani, Bangladeshi and Chinese) might have a criteria. All DSM-III-R studies and four of the DSM-IV
120 Eur J Pediatr (2007) 166:117–123

studies [20, 25, 36, 49] reported prevalence rates from 2.2– prevalence of ADHD-HI symptoms decreased after the
8.9%. The two remaining DSM-IV studies reported high preschool years, whereas the ADHD-I type symptoms
prevalence rates of 11.3% [42] and 16.1% [45]. Twenty- increased dramatically.
nine studies [1, 3, 6–8, 12–14, 18, 19, 21–23, 26, 27, 31,
32, 34, 39–41, 44, 47, 48, 51, 54, 56–58] have used Clinical impairment Assessment of clinical impairment may
informants from a single setting and reported higher well contribute to variations in prevalence rates. Wolraich
prevalence rates (2.8–17.8%). Eleven of them [6, 7, 12, et al. reported ADHD prevalence rate of 16.1% in a
23, 26, 31, 32, 40, 51, 54, 57] reported rates higher than the school population in the USA by using DSM-IV criteria,
upper limit of 9%, which was suggested by almost all the but if the diagnosis of ADHD included symptoms count
two-setting studies. As was seen with two-setting studies, and poor classroom functioning as a measure of
one-setting studies using DSM-IV criteria [6–8, 14, 18, 23, impairment, the prevalence of ADHD would have fell
27, 31, 39, 40, 44, 56, 57] reported higher rates (range, 5.8 to 6.8% [56]. Similarly, in the studies by Shaffer et al.
to 17.8) than these using DSM-III-R criteria (range, 2.8% to and Graetz et al. when clinical impairment of children was
15.1%) [3, 6, 12, 13, 19, 21, 26, 32, 34, 41, 47, 48, 51, 54, taken into account, the prevalence of ADHD dropped
57, 58]. from 6.5% to 5.1% and from 7.5% to 6.8%, respectively
[27, 47].
Definition of the disorder Modifications in the Diagnostic
and Statistic Manual (DSM) of Psychiatric Disorders
definition seemingly resulted in changes in the prevalence’s
rate of ADHD [6]. As already shown, ADHD prevalence was Discussion
higher with DSM-IV criteria than with DSM-III-R, probably
due to recognition of the disorder subtypes. This possibility As clearly shown from this overview, the prevalence of
is strongly supported by two studies which applied both ADHD has been reported with great variations among
DSM-III-R and DSM-IV criteria to the same population and different studies. Population variables that definitely affect
demonstrated great differences in prevalence rates, 7.3% vs. the prevalence rates include gender, age and population
11.4% and 10.9% vs. 17.8%, respectively [6, 57]. sample, i.e., community or clinic cohorts. Methodology
features that can affect the findings include one-or two-
Prevalence of ADHD subtypes As shown in Table 2, the setting design, DSM-III-R or DSM-IV criteria and clinical
majority of the studies have suggested that the predomi- impairment evaluation. As a result of these complex
nantly inattentive type (ADHD-I) is the more common form influences, a definite prevalence of ADHD seems impossi-
of ADHD, followed by combined (ADHD-C) and hyper- ble to be achieved, unless studies of very similar design are
active-impulsive type (ADHD-HI). The proportion of girls employed. The application of DSM-IV criteria and empha-
with ADHD-I symptoms is higher than in other ADHD sis on the subtypes of ADHD seems to have lead to an
subtypes [6, 25, 31, 39, 42, 56, 57]. ADHD is more increase in the frequency of the disorder. Additionally, the
prevalent among males in all three subtypes [6, 18, 25, 27, DSM-IV guidelines are rather vague in defining impairment
40, 42, 56, 57]. Nolan et al. (2001) found that the and clinically significant impairment. As prevalence of

Table 2 Prevalence of ADHD subtypes in 11 studies world-wide, 1995–2004

Study ADHD-IA (%) ADHD-HI (%) ADHD-C (%) ADHD total (%)

Baumgaertel et al. 1995 9.0 3.9 4.8 17.8

Wolraich et al. 1996 5.4 2.4 3.6 11.4
Gaub and Carlson 1997 4.5 1.7 1.9 8.0
Wolraich et al. 1998 8.8 2.6 4.7 16.1
Hudziak et al. 1998 4.0 2.2 3.7 9.9
Gomez et al. 1999 1.6 0.2 0.6 2.4
Greatz et al. 2001 3.7 1.9 1.9 7.5
Nolan et al. 2001 9.9 2.4 3.6 15.8
Montiel-Nava 2002 1.14 0.35 5.7 7.19
Pineda et al. 2003 4.8 0.3 6.4 11.5
Ersan et al. 2004 2.6 3.3 2.2 8.1

ADHD: Attention Deficit Hyperactivity Disorder; ADHD-IA: Attention Deficit Hyperactivity Disorder, Predominantly Inattentive Type; ADHD-
HI: Attention Deficit Hyperactivity Disorder, Predominantly Hyperactive-Impulsive type; ADHD-C: Attention Deficit Hyperactivity Disorder,
Combined Type
Eur J Pediatr (2007) 166:117–123 121

ADHD decreases with clinical assessment, more research that teachers tended to rate black children higher than white
data is needed to improve the existing confusion on the [17].
assessment of impairment. Variations in prevalence of ADHD across studies seem
Several studies have reported dramatic decline in ADHD to be greatly influenced by the choice of informants.
prevalence in adolescents. Hill and Schoener (1996) Reasonably the child is not a reliable source of information.
examined nine prospective studies in which cohorts of Children younger than 12 years of age seem to have low
children with ADHD were formed and then re-examined test-retest reliability for both internalizing and externalizing
for persistence of ADHD 4–16 years later, and concluded symptoms, even over a short period of time [46]. Self-
that prevalence of ADHD appears to decline about 50% reported symptoms for youth with ADHD are usually so
every 5 years [30]. under-reported that they are of very limited use. Teachers’
Furthermore, in a prospective follow-up by Barkley contributions are substantial, given that they daily observe
et al. (1990), among 123 children who met diagnostic many children at the same developmental level and in the
criteria for ADHD at 4 to 12 years of age, 71.5% still same environment. Parents are also valuable informants by
met criteria 8 years later, with attention problems being having witnessed child’s behaviour for several years in
the most common symptoms. Additionally, Gittelman et multiple settings. Contrary to earlier versions, DSM-IV
al. [24] compared in a prospective study 101 male diagnostic criteria require evidence of symptoms in two
adolescents and youths who had been diagnosed as settings (e.g., school and home), and the use of multiple
hyperactive in childhood (6–12 years) with 100 normal informants has become a basic epidemiological tool [49].
controls and found that full ADHD syndrome persisted in Thus the application of DSM-IV criteria to screen children
31% vs. 3% in the controls. In a similar study Manuzza et in different settings may narrow the width of differences in
al. (1991) assessed 94 young adults males (mean age, 18 prevalence estimations.
years), who had been diagnosed as hyperactive at 5 to Another important issue regarding differences in
11 years of age. At follow-up 22% met full DSM-III ADHD prevalence is the diagnostic method used in
criteria for ADDH, while 15% presented with symptoms studies worldwide. After 20–30 years of different
of inattention and impulsivity, but not hyperactivity [38]. operational definitions DSM-IV and ICD-10 [55] in their
Similarly, Hart and colleagues assessed annually and for recent versions, conclude in an almost identical symptom-
4 years 106 boys (mean age, 9.4 years), which met DSM- atology of the disorder. However, they still use different
III-R criteria for ADHD. They concluded that hyperactiv- names for the disorder, i.e., ADHD according to DSM-IV
ity-impulsivity symptoms declined with increasing age, and hyperkinetic disorder (HKD) according to ICD-10,
but inattention symptoms did not [29]. The association of and there are major differences in the diagnosis of the
age with decline in total ADHD symptoms was proved in disorder, potentially leading in considerable prevalence
the study of Biedreman et al. (2000), who measured discrepancies.
symptoms of ADHD in 128 boys fivefold over 4 years. The main differences between DSM-IV and ICD-10 are
They pointed that symptoms of inattention remitted for related to the concomitance of the three domains (inatten-
fewer subjects than did symptoms of hyperactivity or tion, hyperactivity and impulsivity), the exclusion of
impulsivity [9]. comorbidity and the degree of pervasiveness. ICD-10
These studies suggest that there is a substantial decline criteria require a full set of symptoms in all three domains,
over time in the number of individuals who retain clinically while DSM-IV recognizes three subtypes of the disorder, in
significant symptoms of ADHD and that inattention the case symptoms are from one domain. A diagnosis of
symptoms are more likely than hyperactive symptoms to HKD is, thus, most congruent with a DSM-IV diagnosis of
persist into adulthood. It remains unclear, though, how this ADHD combined type without the presence of comorbidity.
decline occurs. In contrast to DSM-IV, ICD-10 uses the presence or
ADHD prevalence may be culture dependent, as what is absence of conduct disorders as the basis of the main
considering abnormal in one culture may be more accept- subdivision of HKD. Furthermore, in their study Swanson
able in another, and culture may affect the report by et al. suggested that ADHD prevalence according to DSM
informants (parent and teachers) or clinicians. Mann et al. is 5–10% in the general population whereas this frequency
(1992) investigated the differences among mental health is 1–2% with ICD tradition, which restricts diagnosis to the
professionals in China, Indonesia, Japan and USA differed syndrome with limited comorbidity [52].
in rating of ADHD and found that Chinese and Indonesian Studies using ICD-9 and ICD-10 and DSM-III criteria
clinicians gave significantly higher scores for hyperactivity were not included in the present analysis. Nevertheless,
than Japanese and American colleagues did [37]. Student child and adolescent populations from all over the world
ethnicity has been suggested to affect the rating of ADHD were represented in the analyzed studies. As shown from
symptoms [43] and Epstein and colleagues (1998) pointed this review, almost all the two-setting studies, although
122 Eur J Pediatr (2007) 166:117–123

performed in different countries worldwide, result in 14. Cuffe SP, Moore CG, McKeown RE (2005) Prevalence and
ADHD prevalence rates from 2.2% to 8.9%, and the correlates of ADHD symptoms in the national health interview
survey. J Atten Disord 9:392–401
majority of all studies in general indicate prevalence rates 15. DuPaul GJ, Anastasopoulos AD, Power TJ, Reid R, Ikeda
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prevalence among studies worldwide seem to reflect hyperactivity disorder symptoms: factor structure and norma-
methodology differences rather than intrinsic population tive data. J Psych Behav Assessment 20:83–102
16. Elia J, Ambrosini PJ, Rapoport JL (1999) Treatment of attention-
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must be used in the future in order to draw firm conclusions 17. Epstein JN, March JS, Conners CK, Jackson DL (1998) Racial
on the true prevalence of ADHD. differences on the conners teacher rating scale. J Abnorm Child
Psychol 26:109–118
18. Ersan EE, Dogan O, Dogan S, Somer H (2004) The distribution of
symptoms of attention-deficit/hyperactivity disorder and opposi-
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