To conserve space in the print version of the journal, the technical details of the meta-analysis are provided in

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1 1 PREVALENCE OF DSM-IV ATTENTION DEFICIT/HYPERACTIVITY DISORDER SUPPLEMENTAL MATERIALS To conserve space in the print version of the journal, the technical details of the meta-analysis are provided in these supplemental materials. The first section of the materials describes the methodology for the literature search and meta-analysis. Supplement Table 1 then provides a summary of each of the studies that was included in the meta-analysis, and Supplement Tables 2-11 list all individual studies and prevalence estimates that were used to estimate the corresponding summary prevalence estimates included in Table 1 in the main paper. The final section of the supplemental materials includes full citations for all studies that were included in the meta-analysis or cited in these supplemental materials. Methodology for the Literature search Inclusion criteria The literature search was completed as part of a larger meta-analysis of the validity of DSM-IV ADHD symptom dimensions and subtypes [87]. Because DSM-IV was published in 1994, computer searches of were performed for the years in the Pubmed, PsycINFO, Educational Resources Information Center (ERIC), and Social Sciences Citation Index databases. All studies with keyword ADHD were selected, and the terms ADHD, ADD, and attention deficit disorder were also cross-referenced separately with DSM-IV, reliability, internal consistency, prevalence, validity, impairment, comorbidity, factor, subtypes and (combined or inattentive or inattention or hyperactive-impulsive or hyperactivity-impulsivity). Tables of contents of journals that commonly publish articles on ADHD were reviewed for the same time period. These were American Journal of Medical Genetics (Neuropsychiatric Genetics), American Journal of Psychiatry, Archives of Clinical Neuropsychology, Archives of General Psychiatry, Behavioral and Brain Functions, Biological Psychiatry, Child Neuropsychology, Child Psychiatry and Human Development, Development and Psychopathology, Developmental Neuropsychology, European Child and Adolescent Psychiatry, Journal of Abnormal Child Psychology, Journal of Abnormal Psychology, Journal of the American Academy of Child and Adolescent Psychiatry, Journal of Attention Disorders, Journal of Child Neurology, Journal of Child Psychology and Psychiatry, Journal of Clinical Child and Adolescent Psychology, Journal of Consulting and Clinical Psychology, Journal of Developmental and Behavioral Pediatrics, Journal of Learning Disabilities, Journal of Psychopathology and Behavioral Assessment, Journal of the American Academy of Child and Adolescent Psychiatry, Journal of the International Neuropsychological Society, Molecular Psychiatry, Psychiatric Genetics, and Psychological Medicine.

2 2 Finally, the reference list of each paper was reviewed for additional studies, and several additional researchers in the field screened the final list of studies. Studies known to the author that were in press at the time of the literature search were included in the review, but other unpublished studies were excluded due to the expansive published literature on the prevalence of DSM-IV ADHD. Exclusion criteria As described in more detailed previously [87], the search procedures yielded 15,736 articles after removal of duplicates as of the end of A multi-stage review procedure yielded 86 studies that estimated the prevalence of DSM-IV ADHD in children and adolescents, and 11 studies that estimated the prevalence of DSM-IV ADHD in adults. To assess the reliability of the search procedures, a random sample of approximately 20% of the studies were also coded for inclusion or exclusion by a second rater. The raters agreed on over 99.5% of the studies, and all disagreements were resolved by consensus after additional discussion (disagreements primarily occurred when studies defined subtypes based on criteria that were ambiguous and not fully consistent with DSM-IV criteria). Extraction and coding of prevalence estimates from individual studies A coding system was developed to classify each diagnostic algorithm and record each prevalence estimate, and studies were coded separately by two independent raters to assess the reliability of the coding system. Interrater agreement was high (over 99%), with the only disagreements occurring when the methodology of the study was not described in sufficient detail to be certain how the diagnosis was made. In nearly all of these cases the inconsistency between raters was resolved after reviewing previous papers that described the sample in question in more detail. Analyses were also repeated with and without effect sizes from these studies, and the overall pattern of results did not change in any of these cases. As in other statistical approaches, the effect sizes in a meta-analysis are assumed to be independent, so each study must contribute only one effect size to a specific analysis [88-90]. Consistent with this assumption, most papers reported prevalence estimates based on a single diagnostic algorithm that was used to define ADHD for the study. However, a subset of studies compared prevalence rates based on different diagnostic algorithms. If a single study reported prevalence based on different algorithms, the data from the study were included in the meta-analysis of each of the algorithms, but a study was never included twice in the same analysis. To test the sensitivity of this decision, analyses were conducted with and without studies that reported prevalence based on different diagnostic algorithms, and there were no significant changes in the overall pattern of results.

3 3 Calculation of overall effect sizes Summary prevalence estimates were calculated using the Comprehensive Meta-analysis statistical package [91]. For each analysis the overall weighted estimate and corresponding 95% confidence interval is reported in Table 1 in the main paper. Supplement Tables 2-11 list all effects that were included in each overall effect size estimate, and also provide a summary of analyses used to test for publication bias and heterogeneity among the effects. Heterogeneity of effects When the individual effect sizes in a specific meta-analysis are homogeneous, an overall effect size can be estimated with a fixed effects model that simply weights the effect size from each study by the corresponding sample size [92]. However, fixed effects models make the strong assumption that any differences in effect sizes among the studies are due entirely to sampling error. If there is significant heterogeneity among studies due to systematic differences in study populations, experimental design, measures, or other study procedures, the prevalence estimate and corresponding confidence interval obtained from the fixed effects model may be biased, and a random effects model is more appropriate [93]. Two methods were used to test for heterogeneity among the effects in each analysis. Cochran s Q statistic is an estimate of the variability of individual effect sizes around the overall estimated effect size that takes a Χ 2 distribution with one less degree of freedom than the total number of effects in the analysis [94]. We also calculated I 2, a more intuitive measure that quantifies the percentage of the overall effect size that is attributable to heterogeneity among the effects [95]. Significant heterogeneity among the effects was observed in the majority of the analyses. Due to this pervasive heterogeneity, the more conservative random effects model was used for all analyses [93]. The random effects model adjusts for heterogeneity by weighting each effect size by both the inverse variance of the sample and an additional weight based on Q. For analyses with low heterogeneity Q is also low and the additional weight goes to zero, in which case the fixed effects and random effects models yield identical results. In addition to the use of random effects models, several approaches were used to identify the source and impact of any significant heterogeneity that was detected among the effects. First, the distribution of effects was examined to test whether heterogeneity was attributable to a small number of outlying values at either end of the distribution of effect sizes. Effects with a significant standardized residual (P <.05) were identified as potential outliers, and analyses were conducted again without these effects to examine the sensitivity of the overall results to these outlying values. In most cases significant heterogeneity was explained by a single or small number of outlier effect sizes, and in nearly all of these

4 4 cases the point estimate of the overall effect size changed minimally when these outlier effects were excluded. Specific results of heterogeneity analyses are summarized in the supplemental tables. Prevalence estimates based on a small number of effects Although many prevalence estimates in the meta-analysis were based on 15 or more effect sizes, for several specific diagnostic algorithms only a handful of estimates were available. A recent paper provided a cogent summary of the strengths and weaknesses of different approaches for the synthesis of results when only a small number of studies are available [96]. The authors first assert that the primary conclusion when a meta-analysis is underpowered is that more evidence is required. Indeed, the current results suggest that additional research is needed regarding the prevalence of ADHD based on several widely-used diagnostic algorithms, including the or-rule used in the DSM-IV field trials. After underscoring this key point, the authors argue that even when the number of studies is small, a meta-analysis is still a better approach than other methods that are often used to synthesize the results of a small number of studies [96]. Alternative approaches include qualitative statements regarding the similarity of effects across studies or broad summary statements about the overall conclusions that should be drawn from studies that were deemed too heterogeneous to combine for meta-analysis. These approaches involve subjective judgments based on internal rules that may be prone to bias and are unlikely to be transparent to the reader. While the utility of meta-analysis is also constrained by a small number of available studies, several considerations support its use even in these scenarios. Perhaps most importantly, the meta-analytic approach is more transparent and less susceptible to bias than alternative descriptive approaches. The greater degree of uncertainty in meta-analyses of a small number of studies is explicitly reflected in a large standard error and wider confidence interval around the point estimate of the effect size. The formal synthesis of results from a small number of studies may also provide important preliminary information about issues that have received relatively little research attention, and the list of available effect sizes helps to underscore explicitly the paucity of relevant data that are available. Therefore, to provide a comprehensive summary of the literature, the supplemental tables include effect sizes from all individual studies that estimated prevalence of DSM-IV ADHD, and meta-analytic procedures were used to estimate prevalence rates if at least two studies used a diagnostic approach that was sufficiently similar to allow pooled analyses. Nonetheless, it is also critical to emphasize that prevalence estimates derived from meta-analyses of a small number of studies should be considered preliminary results that must be interpreted with caution.

5 5 Publication and other selection biases In the context of meta-analysis, bias occurs if the studies included in the review are systematically nonrepresentative of the total population of studies relevant to the question of interest (see [97] for a comprehensive summary of different aspects of bias in meta-analyses). The type of bias discussed most frequently is publication bias, which typically occurs if studies that report significant results are more likely to be published than studies that report nonsignificant results. A related issue arises if published studies only report results of analyses that were significant, and do not report analyses of other measures that yielded nonsignificant results. Other forms of reporting bias may occur if the same result is published more than once or if results are published in journals that are not widely cited and are not captured by typical search procedures. The remainder of this section briefly summarizes the specific methods that were used to test for bias and estimate its impact on the results of the meta-analysis. Egger's multiple regression test. This method tests whether there is evidence of significant publication bias that may change the overall point estimate of the effect size [100]. A regression model is fitted to the association between the magnitude and precision of the observed effect sizes included in the analysis. If there is no publication bias (i.e., if all completed studies are included in the analysis) these two variables should be unrelated, whereas a significant value for the regression intercept indicates the possibility of publication bias. Trim and fill. The trim-and-fill procedure is a two-step procedure that first evaluates the extent of any bias, then estimates the true effect size and standard error that would be obtained if the missing studies had been included in the analysis [101]. The first step of the trim-and-fill procedure is based on the same idea that underlies the funnel plot, a graphical approach that has often been used to screen qualitatively for evidence of bias in meta-analyses. An example of a funnel plot from the current meta-analysis is provided in Figure 1. Each unfilled circle in the figure represents the point estimate of the prevalence of ADHD-H from a single study. The x-axis of the plot indicates the effect size (for statistical reasons prevalence rates are converted to logit event rates prior to metaanalysis), and the vertical axis indicates the corresponding standard error for each effect (a direct function of sample size). In the absence of bias, the scatterplot of effects should be distributed symmetrically around the overall effect size, and the distribution should be shaped like an inverted funnel due to the less precise estimates obtained in the smaller samples at the bottom of the chart.

6 6 In contrast, an asymmetric distribution of effects suggests that some effects are missing. The trim-and-fill procedure first estimates the number of studies that are missing from one side of the distribution (in the example in Figure 1 three effects were missing from the higher tail of the distribution). The same number of studies are then removed (trimmed) from the other side of the distribution to compensate for the hypothetical missing effects, and the overall point estimate is recalculated. In the example the prevalence estimate was slightly higher after this procedure was completed (3.7% vs. 3.2%). An imputation procedure is then used to estimate the effect size for each of the hypothetical missing studies in the distribution, and these new effects are added to the original distribution (the filled circles in Figure 1). The resulting distribution is then used to calculate the adjusted standard error of the overall effect size if the hypothetical missing effects were included. Summary of the impact of publication / selection bias. For each prevalence estimate that is based on three or more samples, the Supplement Table provides a summary of analyses of heterogeneity and publication bias, including Egger's regression and Trim and Fill procedures. All publication bias analyses were conducted after accounting for heterogeneity among the effects [99]. Trim and fill procedures suggested that at least one effect size was missing from the distribution of effects in 29% of the analyses. However, a relatively small number of distributions were missing more than three effect sizes (11%), and Egger's regression analyses indicated significant bias in only 8% of analyses. Most importantly, when the hypothetical missing effects were added to the distribution as part of the trim-and-fill procedure, the mean change in the point estimate of the prevalence of ADHD was small (0.2%), and no point estimate changed by more than 0.5%. Overall, these results suggest that the substantive conclusions of the review are unlikely to be attributable to publication bias or other sampling biases in the literature search.

7 7 Supplement Table 1 Studies of the prevalence of DSM-IV ADHD included in the meta-analysis Cite # Author / Year Location Age Range Total N Resp. Rate a Exclusion Criteria b Sampling procedures and definition of ADHD [1] Adewuya 2007 Nigeria ,112 92% 1, 2, 5 A random sample was drawn from 192 classrooms in 16 schools in Osun state. If a teacher endorsed three or more ADHD symptoms with impairment on the VADTRS, the child s parent was asked to complete the VADPRS. Items rated as occurring "often" or "very often" were coded as positive symptoms. The operational definition of ADHD required the child to meet full DSM-IV criteria based on parent or teacher ratings and to exhibit at least 3 symptoms of inattention or hyperactivity-impulsivity on the rating by the other reporter. [2] Alloway 2010 UK NR None Classroom teachers in 12 schools rated DSM-IV ADHD symptoms on the ADHDRS-IV. Items endorsed as occurring "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on DSM-IV symptom criteria only. [3] Alqahtani 2010 S. Arabia % None Parent and teachers completed the VADTRS and VADPRS on a random sample of ten children from each classroom in a randomly selected sample of 33 schools in the Assir region. Items rated as occurring "often" or "very often" were coded as positive symptoms, and the prevalence of ADHD was estimated based on DSM-IV symptom criteria only [4] Alyahri 2008 Yemen ,210 89% None Prevalence was estimated based on a one-stage random sample of 203 children in grades 1-4 in a rural district of Lahj province and a two-stage random sample of 1,007 children in the city of Mukalla. In the urban sample all children who screened positive on the SDQ received a full assessment using the DAWBA interview, along with a random sample of 17% of the children who screened negative. In the rural sample the SDQ and DAWBA were completed for all children. Best estimate ADHD diagnoses were made by experienced clinicians based on full DSM-IV criteria. [5] Amador-Campos 2006 Spain % c None Parents and teachers completed DSM-IV ADHD checklists for a random sample of children attending six schools in Barcelona. Items rated as occurring "often" or "very often" were coded as positive symptoms, and the prevalence of ADHD was estimated based on DSM-IV symptom criteria only. [6] Amiri 2010 Iran ,658 NR 1-3, 13, 14 Random proportional cluster sampling was used to draw a random sample of 60 classes in 30 schools in Tabriz. Teachers completed the CTRS-R. Structured diagnostic interviews were then completed with parents and teachers of children with T scores 65 or higher on the CTRS- R, and prevalence was estimated using best estimate diagnoses based on full DSM-IV criteria.

8 Supplement Table 1 Studies of the prevalence of DSM-IV ADHD included in the meta-analysis Supplemental Materials: Prevalence of DSM-IV ADHD 8 Cite # Author / Year Location Age Range Total N Resp. Rate a Exclusion Criteria b Sampling procedures and definition of ADHD [7] Angold 2002 USA % None A random sample was drawn from all children in public school in four counties in North Carolina. ADHD symptoms endorsed on parent- and self-report structured interviews (CAPA) were combined using the or-rule algorithm, and the prevalence of ADHD was estimated based on full DSM-IV criteria. [8] Anselmi 2010 Brazil ,452 81% None Prevalence in a Brazilian birth cohort was estimated using a two-stage sampling procedure. In the screening phase the mothers of 4,452 children completed the SDQ. Individuals with a positive screen (N = 122) and a random sample of those with a negative screen (N = 158) then completed the DAWBA interview. In the rural sample the SDQ and DAWBA were completed for all children. Best estimate ADHD diagnoses were then made by experienced clinicians based on full DSM-IV criteria. [9] Bauermeister 2007 P. Rico ,897 90% None Parent-report and self-report diagnostic interviews were completed with the DISC-IV for one child living in a random sample of households weighted to be representative of the population of children in Puerto Rico in The study compared the prevalence of ADHD subtypes based on different DSM-IV diagnostic criteria. [10] Baumgaertel 1995 Germany , % 6 A convenience sample of 44 teachers in 10 schools in Bavaria voluntarily completing anonymous ratings of all students in their class on the VADTRS. Items rated as occurring "often" or "very often" were coded as positive symptoms, and the prevalence of ADHD was estimated based on DSM-IV symptom criteria only. [11] Benjasuw Thailand NR None Parents of children from a single school completed the CPRS, and follow-up interviews were completed with a DSM-IV interview. Prevalence was estimated based on full DSM-IV criteria. [12] Bird 2006 P. Rico ,353 89% 1, 2 A multistage probability sampling procedure was used to identify a representative sample of children from Puerto Rico. Parents were interviewed with the DISC-IV, and ADHD diagnoses were made based on full diagnostic criteria, with the exception that impairment was only required in one domain. [12] Bird 2006 USA ,138 81% 1, 2 A multistage probability sampling procedure was used to identify a representative sample of Puerto Rican children in South Bronx, New York. Parents were interviewed with the DISC-IV, and ADHD diagnoses were made based on full diagnostic criteria, with the exception that impairment was only required in one domain. [13] Bohlin 2004 Sweden % None A random sample of children was drawn from the Swedish Population Register. Parents completed the FTF, and the prevalence of ADHD was estimated based on DSM-IV symptom criteria only.

9 Supplement Table 1 Studies of the prevalence of DSM-IV ADHD included in the meta-analysis Supplemental Materials: Prevalence of DSM-IV ADHD 9 Cite # Author / Year Location Age Range Total N Resp. Rate a Exclusion Criteria b Sampling procedures and definition of ADHD [14] Campbell 2009 USA 1st grade 1,082 79% None Data were drawn from the NICHD Study of Early Child Care and Youth Development, a longitudinal study of a birth cohort drawn from 10 sites around the country. Symptoms rated as "pretty much" or "very much" a problem were coded as positive symptoms, and prevalence was estimated based on DSM-IV symptom criteria only, with the exceptions that the prevalence of ADHD-H was not reported, and children who exhibited six or more symptoms of inattention and five symptoms of hyperactivity-impulsivity were not included in any subtype group. [15] Canino 2004 P. Rico See description of [9]. [16] Carlson 1997 USA ,984 93% None Teachers completed anonymous ADHD ratings on the SNAP-IV for all children in nine elementary schools in Texas selected due to low socioeconomic status. Items rated as occurring "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on DSM-IV symptom criteria only. [17] Cho 2009 S. Korea ,651 66% None One elementary school was selected randomly from each of six sections of Seoul, and ten classrooms were randomly selected from each school. Parents of all children in each class were interviewed using the DISC-IV, and prevalence was estimated based on full DSM-IV criteria. [18] Costello 2003 USA ,420 79% None A random sample was drawn to be representative of the population of children in 11 counties in western North Carolina. A parent-report structured interview (CAPA) was used to estimate the prevalence of ADHD based on full DSM-IV criteria. [19] Döpfner 2008 Germany ,452 68% None A random sample was selected from a larger nationally representative sample of 17,641 children. A DSM-IV ADHD rating scale was completed by parents, and items rated as "predominantly true" or "especially true" were coded as positive symptoms. Prevalence estimates based on different diagnostic algorithms were compared. [20] DuPaul 1998 USA ,000 85% None Teachers in 31 school districts completed anonymous ratings of one girl and one boy on the ADHDRS (N = 4,009). Items rated as occurring "often" or "very often" were coded as positive symptoms, and the prevalence of ADHD was estimated based on symptom criteria only in a random sample of 2,000 children selected from the total screening sample. [21] DuPaul 2001 USA NR None Students in undergraduate psychology courses at three universities completed self-report ratings of current DSM-IV ADHD symptoms on the YARS. Items rated as present "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on DSM- IV symptom criteria only.

10 Supplement Table 1 Studies of the prevalence of DSM-IV ADHD included in the meta-analysis Supplemental Materials: Prevalence of DSM-IV ADHD 10 Cite # Author / Year Location Age Range Total N Resp. Rate a Exclusion Criteria b Sampling procedures and definition of ADHD [21] DuPaul 2001 N. Zealand NR None Volunteers from undergraduate psychology courses at the University of Otago completed self-report ratings of current DSM-IV ADHD symptoms on the YARS. Items rated as present "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on DSM-IV symptom criteria only. [21] DuPaul 2001 Italy NR None Students in undergraduate psychology courses at Universita di Padova completed selfreport ratings of current DSM-IV ADHD symptoms on the YARS. Items rated as present "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on DSM-IV symptom criteria only. [22] Eapen 2003 UAE % None A random sample of households was selected from all households in Al Ain, a medium size city in which one-third of the population are UAE citizens. Parent-report and self-report interviews (K-SADS) were completed for children from a random sample of the families with UAE citizenship, and a best estimate diagnosis of ADHD was made based on full DSM-IV criteria. [23] Egger 2006 USA 2-5 1,073 70% 1, 2, 12 A two-stage sampling procedure was used to estimate the prevalence of ADHD among children served by a single pediatric Primary Care clinic in North Carolina. In the screening stage all parents completed the CBCL. Parents of all children with scores in the top 30% of the population on the CBCL Total Problems scale completed a structured diagnostic interview (PAPA), along with the parents of a random sample of 20% of children with scores below the top 30% on the CBCL. Responses on the PAPA were used to estimate the prevalence of ADHD based on full DSM-IV diagnostic criteria. [24] Ersan 2004 Turkey ,415 71% None The sampling frame included all children attending a random sample of 8 elementary schools in Sivas, a city with lower mean socioeconomic status than the overall mean for Turkey. One reporter completed an unspecified measure of ADHD symptoms regarding each child (890 parents, 261 teachers, 73 other immediate family members, and 201 unidentified individuals), and the prevalence of ADHD was estimated based on DSM-IV symptom criteria only. [25] Faraone 2005 USA > % None Random digit dialing was used to identify a random sample of adults, and DSM-IV ADHD symptoms were assessed via self-report interview. Items that were reported to occur "often" were coded as positive symptoms, and the prevalence of ADHD was estimated based on DSM-IV symptom criteria only.

11 Supplement Table 1 Studies of the prevalence of DSM-IV ADHD included in the meta-analysis Supplemental Materials: Prevalence of DSM-IV ADHD 11 Cite # Author / Year Location Age Range Total N Resp. Rate a Exclusion Criteria b Sampling procedures and definition of ADHD [26] Ford 2003 UK ,440 78% None A stratified random sample was selected from a child benefits register which represents 90% of children in Great Britain. Parents, teachers, and children each completed the DAWBA interview. A team of expert clinicians then reviewed all information and assigned a best estimate diagnosis of ADHD based on full DSM-IV criteria. [27] Froehlich 2007 USA ,082 79% None A multistage probability sampling procedure was used to select a representative sample of the noninstitutionalized US population. A DISC-IV interview was administered to all parents to estimate the prevalence of ADHD based on full DSM-IV diagnostic criteria. [28] Gadow 1997 USA NR d 2, 5-7, 9 Parents completed anonymous ratings of ADHD symptoms on the ECI for children attending a convenience sample of 11 private preschool and day care centers and 4 Head Start programs in New York. Items rated as occurring "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on DSM-IV symptom criteria only. [29] Gadow 1998 USA % 6 Parents completed anonymous ratings of ADHD symptoms on the Adolescent Symptom Inventory (ASI) for a sample of adolescents attending a middle school and a high school in New York. Items rated as occurring "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on symptom criteria only. [30] Gadow 1999 USA NR 6 Parents of a subset of the sample completed anonymous ratings of ADHD symptoms on the CSI during their child s regular visit to the pediatrician (N = 263), and the remainder were mailed the rating scale by one of a convenience sample of three schools in New York. Symptoms rated as occurring "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on symptom criteria only. [31] Gau 2005 Taiwan ,070 24% None A two-stage sampling procedure was used to estimate the prevalence of ADHD in a convenience sample of 2 schools in South Taiwan. All participants completed a screening version of the K-SADS-E. All participants who screened positive completed the full self-report interview, along with 10% of the students who screened negative. A team of three clinicians then assigned a consensus ADHD diagnosis based on the full K-SADS-E interview and collateral information from the TRF. [32] Gaub 1997 USA See description of [16]. In this report only symptoms rated as occurring "very often" were coded as positive symptoms, and prevalence was estimated based on symptom criteria only. [33] Ghanizadeh 2008 Iran ,600 80% 1, 2, 5, 11 Parents of all children in a stratified random sample of schools and classrooms were asked to complete the CSI. Symptoms rated as occurring "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on symptom criteria only.

12 Supplement Table 1 Studies of the prevalence of DSM-IV ADHD included in the meta-analysis Supplemental Materials: Prevalence of DSM-IV ADHD 12 Cite # Author / Year Location Age Range Total N Resp. Rate a Exclusion Criteria b Sampling procedures and definition of ADHD [34] Gimpel 2000 USA NA None Parents completed the ADHDRS regarding children attending a convenience sample of 44 day care centers in a city and small town. Symptoms rated as occurring "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on symptom criteria only. [35] Gomez 1999 Australia ,275 66% e None The sample included all children attending a random sample of 16 schools in Melbourne and Ballarat. Parents and teachers completed the ADHDRS for all consenting participants in each school. Symptoms rated as occurring "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on symptom criteria only. [36] Gomez 2008 Malaysia % None Parents of children from 14 randomly selected schools completed the DBRS. Symptoms rated as occurring "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on symptom criteria only. [37] Graetz 2001 Australia ,566 70% None A multistage probability sample was obtained that is representative of the population of Australia. Parents of all individuals in the sample completed the DISC-IV interview, and the prevalence of ADHD was estimated based on full DSM-IV diagnostic criteria. [38] Gul 2010 Turkey ,126 75% None A multistage stratified random sample of six schools was drawn from all schools in Trabzon. Parents and teachers completed a rating scale that included the DSM-IV symptoms of ADHD. Symptoms rated as occurring "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on symptom criteria only. [39] Heiligenstein 1998 USA NA None College students were recruited through a variety of procedures, then completed a DSM-IV ADHD rating scale regarding current symptoms. Items endorsed as occurring "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on symptom criteria only. [40] Jané 2006 Spain 3-6 1,104 77% f None The sample included all children in public and private preschools in an urban and a rural area of Catalonia. Parents and teachers rated each child on the ECI. Symptoms rated as occurring "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on symptom criteria only. [41] Kadesjo 2004 Sweden % None A stratified sample of children was selected to be representative of the population of Sweden in Parents of all children completed the FTF Questionnaire, and the prevalence of ADHD was estimated based on symptom criteria only.

13 Supplement Table 1 Studies of the prevalence of DSM-IV ADHD included in the meta-analysis Supplemental Materials: Prevalence of DSM-IV ADHD 13 Cite # Author / Year Location Age Range Total N Resp. Rate a Exclusion Criteria b Sampling procedures and definition of ADHD [42] Kashala 2005 Congo 7-9 1,187 50% g 3, 5, 13 Teacher ratings on the DBD were obtained for children in 10 schools selected randomly from all consenting schools in Kinshasa, the largest city in the country. Symptoms rated as occurring "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on symptom criteria only. [43] Katusic 2005 USA M = 18 5,718 67% 1-3 The sample is a birth cohort of children who remained in Rochester, MN after age 5. A best estimate diagnosis was determined for each child in the cohort after an extensive review of school and medical records. ADHD diagnoses were based on all DSM-IV criteria except age of onset, because this was not reliably available in the records. [44] Kessler 2006 USA ,199 71% None A screen for adult ADHD was included in a probability subsample of respondents in the National Comorbidity Survey Replication. Follow-up interviews were conducted with 154 respondents, and multiple imputation procedures were used to estimate prevalence based on full DSM-IV diagnostic criteria. [45] Kroes 2001 Netherl ,317 51% None A two-stage sampling procedure was used to identify a sample of children in second grade in Limburg. All children scoring above the 95th percentile on CBCL Attention Problems were invited to complete the full study, and a child who scored below the 95th percentile cutoff was matched to each child above the cutoff on sex, age, and school. The prevalence of ADHD was estimated based on full DSM-IV diagnostic criteria as assessed by a parent-report interview (ADIKA). [46] LaVigne 2009 USA % 1, 2 Families were approached through 13 public schools and 23 primary care pediatric practices in Chicago and invited to participate. Parents completed the DISC-IV, and the effect of different diagnostic algorithms on prevalence were examined. [47] Leung 2008 China NA None The sample included students in 7th - 9th grade in a random sample of 28 mainstream high schools in Hong Kong. ADHD symptoms endorsed in parent-report and self-report structured interviews (DISC-IV) were combined using the or-rule, and ADHD prevalence was estimated based on full DSM-IV diagnostic criteria. [48] Levy 2005 Australia ,356 48% h 1-3, 7, 9 An unselected sample of twins was recruited through the Australian Twin Registry, and parents rated each child on the ATBRS. Symptoms rated as occurring "often" or "very often" were coded as positive symptoms. Prevalence was estimated based on symptom criteria only in this paper, and Rasmussen et al. [64] reported prevalence based on full DSM-IV criteria.

14 Supplement Table 1 Studies of the prevalence of DSM-IV ADHD included in the meta-analysis Supplemental Materials: Prevalence of DSM-IV ADHD 14 Cite # Author / Year Location Age Range Total N Resp. Rate a Exclusion Criteria b Sampling procedures and definition of ADHD [49] Magnússon 1999 Iceland % i None A random sample of children was drawn from first and third grade classrooms in five schools in Reykjavik, and parents and teachers rated each child on the ADHDRS. Symptoms rated as occurring "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on symptom criteria only. [50] McKee 2008 USA ,077 NR None Entering first-year students in three private colleges completed self-report ratings of DSM-IV ADHD symptoms as part of their orientation. Items were rated on a three-point scale with anchors "disagree", "undecided", and "agree". The number of DSM-IV symptoms endorsed as "agree" were summed, and prevalence was estimated based on symptom criteria only. [51] Merrell 2001 UK 5-7 4,148 NR None A sample was drawn at the beginning of formal education that was representative of children in England (schools paid a fee to participate). Teachers completed a rating scale that included the DSM-IV symptoms of ADHD, and were asked to indicate for each child which symptoms were considerably more frequent than that of children the same gender and developmental level. ADHD was then defined by symptom criteria only. [52] Meyer 2004 S. Africa ,094 95% None Participants were recruited from a convenience sample of 20 primary schools in Limpopo Province. Schools were required to have electricity and to be accessible by road. Teachers rated each child on the DBD, symptoms rated as occurring "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on symptom criteria only. [53] Montiel 2008 Venezuela ,535 81% 1, 3 A two-stage sampling procedure was used to estimate the prevalence of ADHD in a random sample of children attending schools in Maracaibo. All children in a randomly selected subset of schools were screened using the Conners Parent and Teacher Rating Scales. Parents of children with T scores greater than 70 on the CPRS or CTRS completed the DISC-IV interview, along with the parents of a random sample of children with T scores below 65. The prevalence of ADHD was estimated using full DSM-IV criteria assessed by the structured interview and C-GAS. [54] Mugnaini 2006 Italy 6-7 1,891 78% 1, 2, 5 Teachers completed the VADTRS on a random sample of children selected from 49 public schools in Florence.. Items rated as occurring "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on full DSM-IV diagnostic criteria. [55] Murphy 1996 USA NR None A sample of 720 adults applying for or renewing their driver's licenses completed self-report rating scales for current symptoms of ADHD and retrospective recall of childhood symptoms. Items rated as occurring "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on symptom criteria only.

15 Supplement Table 1 Studies of the prevalence of DSM-IV ADHD included in the meta-analysis Supplemental Materials: Prevalence of DSM-IV ADHD 15 Cite # Author / Year Location Age Range Total N Resp. Rate a Exclusion Criteria b Sampling procedures and definition of ADHD [56] Neumann 2005 USA ,472 49% 2, 8 Twin pairs in Missouri were identified through birth records, and a 2-stage screening procedure was used to assess pairs who were not already participating in the separate study described below (72). Initial screening interviews were completed by telephone for the entire sample (N = 5,007), followed by structured diagnostic interviews of parents and twins in 564 families who met screening criteria and a comparison group of 183 families who did not meet the screening criteria. The structured interviews were used to estimate the prevalence of ADHD based on full DSM-IV criteria. [57] Nolan 2001 USA NR 6, 10 j Teachers completed anonymous ECI ratings for children attending a convenience sample of 11 private preschool and day care centers and 4 Head Start programs. Items rated as occurring "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on symptom criteria only. [57] Nolan 2001 USA ,520 NR 6, 10 k Teachers from regular education classrooms in 16 schools in Missouri, Wisconsin, and New York voluntarily completed anonymous CSI [30, 102] ratings for up to 10 children per classroom. Items rated as occurring "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on symptom criteria only. [57] Nolan 2001 USA ,072 NR 10 Teachers completed anonymous ratings on the ASI [29] for a sample of adolescents attending a convenience sample of regular education classrooms in 6 public schools from districts in Missouri, Wisconsin, and New York. Items rated as occurring "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on symptom criteria only. [58] Owens 2003 USA % none Parents and teachers completed DBD ratings for all children in fourth through sixth grade in a convenience sample of 9 schools in Indiana. The or-rule algorithm was used to combine parent and teacher ratings of ADHD symptoms with items rated as occurring "very often" considered a positive symptom, and the prevalence of ADHD was estimated based on symptom criteria only. [59] Petersen 2006 Denmark 7-8 5,563 42% 10 A two-stage sampling procedure was used to estimate the prevalence of ADHD in a random sample of children attending 34 schools in the county of Funen. All children with significantly elevated scores on the CBCL and a random sample of children without elevated scores completed parent-report and self-report structured diagnostic interviews (K-SADS; N = 373). Final ADHD diagnoses were based on full DSM-IV diagnostic criteria.

16 Supplement Table 1 Studies of the prevalence of DSM-IV ADHD included in the meta-analysis Supplemental Materials: Prevalence of DSM-IV ADHD 16 Cite # Author / Year Location Age Range Total N Resp. Rate a Exclusion Criteria b Sampling procedures and definition of ADHD [60] Pineda 1999 Colombia % 1, 2, 6, 11 A clustered random sample (based on SES, gender, and age) was selected from all children attending schools in Manizales City. Parents rated each child on a DSM-IV ADHD rating scale, items rated as occurring "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on symptom criteria only. [61] Pineda 2003 l Colombia % 1-6, 9, A clustered random sample of children (clusters based on SES, gender, and age) was selected from a random sample of 5 private and 15 public schools in Manizales City. The parent and teacher of each child completed a DSM-IV ADHD rating scale and the short-forms of the CPRS and CTRS, and the parents of children with six or more symptoms of inattention or hyp-imp on the rating scale completed a semi-structured diagnostic interview. A best estimate ADHD diagnosis was made for each child based on full DSM-IV criteria. [62] Ramtekkar 2010 USA ,193 2, 7, 11 Expansion of sample described by [56] to include young adults. [63] Rasmussen 2002 USA Subsample of overall sample described by [72]. [64] Rasmussen 2004 USA See description of [72] and [48]. [65] Rohde 1999 Brazil ,013 99% none A random sample of students was drawn from a clustered random sample of 64 schools in Porto Alegre. All students with 5 or more symptoms of inattention or hyp-imp on a screening assessment completed the full assessment, along with a random sample of those without elevations of inattention or hyp-imp. The second stage included self-report and parent-report interviews, and a best estimate diagnosis of ADHD was made by an experienced clinician based on full DSM-IV diagnostic criteria. [66] Servera 2010 Spain , % 1, 2, 13, 15 Teachers and parents completed the ADHDRS for students in a random sample of classrooms that were randomly selected from a random sample of 16 schools on the island of Majorca. Items rated as occurring "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on symptom criteria only. [67] Skounti 2006 Greece 7 1,285 75% 1, 2, 6 Parents and teachers completed DSM-IV ratings of children in first grade in 55 mainstream public schools in a large city in Crete. Items rated as occurring "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on full DSM-IV criteria.

17 Supplement Table 1 Studies of the prevalence of DSM-IV ADHD included in the meta-analysis Supplemental Materials: Prevalence of DSM-IV ADHD 17 Cite # Author / Year Location Age Range Total N Resp. Rate a Exclusion Criteria b Sampling procedures and definition of ADHD [68] Smalley 2007 Finland ,622 41% 2, 7 As part of a follow-up study of a birth cohort in northern Finland, parents completed the SWAN. Individuals scoring above the 95th percentile on the SWAN inattention or hyperactivity-impulsivity scales were selected for more detailed assessment using the K- SADS-L, along with a control sample with scores below the 90th percentile. Prevalence was estimated for a best estimate diagnosis of ADHD. Participants between the 90th and 95th percentile were not included in additional testing or prevalence estimates. [69] Sprafkin 2007 USA NR None Participants were recruited through social, service, and religious groups in Suffolk County, New York. Anonymous self-report ratings of symptoms during the past six months were completed on the ASRI-4, and the prevalence of ADHD was estimated based on DSM-IV symptom criteria only. [70] Talaei 2010 Iran % None A random sample of 24 classrooms were selected from 12 schools. Parents and teachers completed the Conners Rating Scales, and a clinical interview based on DSM-IV criteria was administered to participants who scored above a screening threshold. Prevalence estimates used a best estimate diagnosis of ADHD based on full DSM-IV criteria. [71] Thabet 2010 Gaza / West Bank NR None A random sample of 16 children was selected from a random sample of 15 schools in the Gaza Strip and 8 schools in Bethlehem and East Jerusalem. Parents and teachers completed a checklist keyed to DSM-IV symptoms, and ADHD was defined based on a best estimate diagnosis. [72] Todd 2001 USA ,036 77% None As part of the Missouri Adolescent Female Twin Study, female twins were identified from state birth records. Parents of each twin completed a structured diagnostic interview (DICA- IV), and full DSM-IV criteria were used to estimate the prevalence of ADHD. [73] Tuvblad 2009 USA ,219 NR 12 Participants were a representative sample of twins from Los Angeles. Parents completed the DSM-IV DISC-IV, and ADHD was defined based on full diagnostic criteria. [74] Volk 2009 USA See description of [72]. This paper reported prevalence based on symptom criteria only. [75] Waschbusch 2007 Canada % None The sample included all students attending a convenience sample of seven elementary schools in Ontario. Mother and father ratings on the ADS-IV were combined using the or-rule, and ADHD status was defined based on full DSM-IV diagnostic criteria with the exception of age-of-onset (the study tested the validity of this criterion).

18 Supplement Table 1 Studies of the prevalence of DSM-IV ADHD included in the meta-analysis Supplemental Materials: Prevalence of DSM-IV ADHD 18 Cite # Author / Year Location Age Range Total N Resp. Rate a Exclusion Criteria b Sampling procedures and definition of ADHD [76] Weiler 1999 USA % None Children in 2nd - 5th grade were recruited from a public school system in Massachusetts, and parents and teachers rated each child on the DRS. Symptoms rated as occurring "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on symptom criteria only. [77] West 2003 Scotland 15 1,860 67% 6 The study used a representative sample of adolescents in mainstream education in western Scotland. Each student completed a self-report diagnostic interview (Voice-DISC-IV), and full DSM-IV criteria were applied to define ADHD status. [78] Willcutt 2007 USA % 1-5, 8 An unselected sample of twin pairs was recruited through a twin birth registry in Colorado. Parents completed ratings of each twin on the DBRS, and prevalence was estimated based on symptom criteria only. [78] Willcutt 2007 Australia % 1-5, 8, 12 Parent ratings were obtained with the DBRS on an unselected sample of twin pairs recruited through twins clubs in New South Wales. Symptoms rated as occurring "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on symptom criteria only. [78] Willcutt 2007 Sweden % 1-5, 8 Parent ratings were obtained with the DBRS on an unselected sample of twin pairs in a registry in Sweden. Symptoms rated as occurring "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on symptom criteria only. [78] Willcutt 2007 Norway % 1-5, 8 Parent ratings were obtained with the DBRS on an unselected sample of twin pairs in a registry in Norway. Symptoms rated as occurring "often" or "very often" were coded as positive symptoms, and prevalence was estimated based on symptom criteria only. [79] Willcutt 2011a USA ,400 67% 1, 2, 4 Students in Introductory Psychology courses completed the Current and Childhood Symptom Inventories, and prevalence was estimated based on full diagnostic criteria. [80] Willcutt 2011b USA ,874 m 65% 1-3, 8, 10 A random sample of schools were selected from five school districts in Colorado, and parents and teachers completed the DBRS for all consenting participants in each school. The study compared the prevalence based on different algorithms for the combination of parent and teacher ratings of ADHD symptoms and functional impairment. [81] Willoughby 2000 USA See description of [18]