Guilherme V. Polanczyk and
Luis Augusto Rohde talk with ScienceWatch.com and
answer a few questions about this month's Fast Breaking
Paper in the field of
Article Title: The worldwide prevalence of ADHD: A
systematic review and metaregression
G;de Lima, MS;Horta, BL;Biederman,
Journal: AMER J PSYCHIAT
Year: JUN 2007
* Univ Fed Rio Grande do Sul, Hosp Cin Porto Alegre, Child
& Adolescent Psychiat Div, ADHD Outpatient Program, Rua
Ramiro Barcelos 2350, BR-90035003 Porto Alegre, RS,
(addresses have been truncated)
Why do you think your paper is highly
Over the past several decades, the scientific community realized that much
more attention should be given to mental disorders affecting children and
adolescents, given their significant and lasting negative impact.
Attention-deficit/hyperactivity disorder (ADHD) is a
prevalent disorder also associated with a wide range of adverse outcomes
across the lifespan, justifying the scientific and lay interest in it.
This study comprehensively addresses the distribution of ADHD around the
world, which is essential for estimating the burden associated with the
disorder. Moreover, we further studied the sources of variability in
prevalence estimates, which gives important clues on the role of
geographical location of the countries included in the study.
Luis Augusto Rohde
It is important to note that the impact of cultural factors in the rates of
ADHD worldwide has been a subject of intense debate. In this sense, this
paper is clearly relevant for policymakers, investigators in the ADHD
field, as well as those interested in research methodology, and
Does it describe a new discovery, methodology, or
synthesis of knowledge?
The paper reports the aggregated prevalence of ADHD across 35 different
countries from all world regions, including studies conducted from 1978 to
2005. Furthermore, we addressed the role of demographic location of the
study in the variability of estimates using a modern statistical
Would you summarize the significance of your paper in
Our study gives an estimate of the worldwide ADHD prevalence aggregating
102 studies, selected according to rigorous criteria. Moreover, since there
is significant variability on estimates across studies, we investigated
which factors are related to this heterogeneity.
Results indicated that different diagnostic criteria among studies,
information source—who reports the symptoms (e.g., teachers or
parents), and whether functional impairment is required or not for the
establishment of the diagnosis, are the major factors related to the
variability of estimates. However, the country where the study was
conducted, which indexes at some extent the cultural background, is not
related to different prevalence estimates.
How did you become involved in this research, and were
there any problems along the way?
We have been studying different aspects of ADHD, from molecular genetics
and pharmacogenetics to epidemiological studies. There was a clear need to
summarize the extensive epidemiological literature on the disorder, but we
were aware that the wide number of studies conducted in such a diverse
number of countries could give us further information about the disorder.
We joined two experts in systematic reviews and meta-regression, Professors
Mauricio Silva de Lima of Eli Lilly, UK and Ireland, and Bernardo Lessa
Horta of the Post-Graduate Program in Epidemiology, Federal University of
Pelotas, Brazil, as well as
Professor Joseph Biederman of Harvard Medical
School, a leader in the ADHD field, and designed the study herein
"This study comprehensively
addresses the distribution of ADHD around the
world, which is essential for estimating the
burden associated with the
It took us approximately two years to carefully review the literature. Two
main problems occurred along the way: electronic searches showed an
important degree of inaccuracy, and original studies varied greatly on the
extent of information they report about their methods.
Where do you see your research leading in the
A wide number of studies have evidenced the significant role of genetic
risk factors in the development of ADHD. Although this study indicates that
cultural background has not played a main role on the worldwide variability
of the occurrence of the disorder, this does not mean that environmental
risk factors do not play a role in its etiological process. We should
proceed with the investigation of genetic risk factors, aggregating
findings from genome-wide association studies and their interaction with
environmental risk factors.
Moreover, further studies must focus on the developmental trajectories of
children with ADHD into adulthood, so we can better understand the disorder
itself in this phase of development, and its relationship with other mental
disorders, such as conduct disorder, substance use, and mood disorders.
Do you foresee any social or political implications for
We can estimate the populational burden associated with ADHD more
accurately with the data generated. Moreover, the conception that this
disorder is more frequent in specific locations than others, due to
cultural or other demographic-associated variables, is not supported by
this study. In this sense, mental health authorities can use our data to
estimate levels of national diagnosis of ADHD in their countries.
Guilherme V. Polanczyk, M.D., Ph.D.
Postdoctoral Research Fellow
SGDP Centre, Institute of Psychiatry
King's College London, UK and
Hospital de Clinicas de Porto Alegre
Luis Augusto Rohde, M.D., Ph.D.
Professor of Child and Adolescent Psychiatry
Federal University of Rio Grande do Sul
Hospital de Clinicas de Porto Alegre