Age, academic performance, and stimulant prescribing for ADHD: a nationwide cohort study

Systematic review and meta-analysis: relative age in attention-deficit/ hyperactivity disorder and autism spectrum disorder

Youngest students in their class, with birthdates just before the school entry cut-off date, are overrepresented among children receiving an Attention-Deficit/Hyperactivity Disorder (ADHD) diagnosis or medication for this. This is known as the relative age effect. This systematic review and meta-analysis summarises the evidence on the influence of relative age on ADHD symptoms, diagnosis and medication prescribing. As no review to date has investigated the association with autism spectrum disorder (ASD) diagnosis, this is also examined. Following prospective registration with PROSPERO, we conducted a systematic review according to the PRISMA guidelines. We searched seven databases: Medline, Embase, PsycInfo, Web of Science Core Collection, ERIC, Psychology and Behavioural Sciences Collection, and Cochrane Library. Additional references were identified from manual search of retrieved reviews. We performed a meta-analysis of quantitative data. Thirty-two studies were included, thirty-one investigated ADHD and two ASD. Younger relative age was associated with ADHD diagnosis and medication, with relative risks of 1.38 (1.36-1.52 95% CI) and 1.28 (1.21-1.36 95% CI) respectively. However, risk estimates exhibited high heterogeneity. A relative age effect was observed for teacher ratings of ADHD symptoms but not for parent ratings. With regard to ASD, the youngest children in their school year were more likely to be diagnosed with ASD. This review confirms a relative age effect for ADHD diagnosis and prescribed ADHD medication and suggests that differences in teacher and parent ratings might contribute to this. Further research is needed on the possible association with ASD.

Relative Age Within School Grade, Including Delayed and Accelerated School Start: Associations With Midlife Psychiatric Disorders, Suicide, and Alcohol- and Drug-Related Mortality

Within a school grade, children who are young for grade are at increased risk of psychiatric diagnoses, but the long-term implications remain understudied, and associations with students who delay or accelerate entry underexplored. We used Norwegian birth cohort records (birth years: 1967-1976, n = 626,928) linked to records in midlife. On-time school entry was socially patterned; among those born in December, 23.0% of children in the lowest socioeconomic position (SEP) delayed school entry, compared with 12.2% among the highest SEP. Among those who started school on time, there was no evidence for long-term associations between birth month and psychiatric/behavioral disorders or mortality. Controlling for SEP and other confounders, delayed school entry was associated with increased risk of psychiatric disorders and mortality. Children with delayed school entry were 1.31 times more likely to die by suicide (95% confidence interval: 1.07, 1.61) by midlife, and 1.96 times more likely to die from drug-related death (95% confidence interval: 1.59, 2.40) by midlife than those born late in the year who started school on time. Associations with delayed school entry are likely due to selection, and results thus underscore that long-term health risks can be tracked early in life, including through school entry timing, and are highly socially patterned.

The effect of school-entry age on health is understudied in low- and middle-income countries: A scoping review and future directions for research

Background

Substantive literature has assessed the impact of starting school at younger ages relative to peers on health in high-income countries (HICs), but there is little evidence from low- and middle-income countries (LMICs). Conclusions drawn from HICs may not apply to different education contexts and health threats. This study maps the empirical evidence on the effect of school-entry age on health in LMICs and identifies directions for future research.

Methods

We conducted a scoping review between August and September 2022 by systematically searching the health sciences, education, economics, psychology, and general sciences literature and included quantitative and qualitative studies. The exposure of interest was relative age for grade defined as starting or progressing through school at a younger or older age compared to peers who are in the same grade. We extracted key characteristics of included studies and summarized their findings. We categorized results into broad health domains which emerged a posteriori from our analyses of included studies, including neurodevelopment and mental health, sexual and reproductive health, non-communicable diseases, and nutrition.

Findings

We identified 8 studies from middle-income countries published between 2017 and 2022. Among those studies, we identified 3 quasi-experimental studies using data from Brazil, Mexico, and Vietnam, and 5 observational studies primarily from Türkiye. Children starting school earlier had an increased risk of being diagnosed with attention deficit hyperactivity disorder, earlier sexual debut and cohabitation, adolescent pregnancy, adolescent marriage, and engaged more frequently in risky behavior compared to children who started school later. Pregnant women who started school younger also had fewer prenatal care visits and experienced more pregnancy complications. Although most studies identified negative health consequences from starting school earlier, the evidence for nutritional outcomes, such as overweight and stunting, was mixed. No studies were identified from low-income countries.

Conclusions

Little is known about the health consequences of school-entry age in low-resource settings. Additional research is needed to investigate the impact of relative age for grade, whether and how these effects persist into adulthood, and to inform strategies that can offset potential disadvantages stemming from school-entry cut-off dates.

Relative Age and Psychotropic Drug Use in Preterm and Term-Born Children and Young Adults

BACKGROUND AND OBJECTIVES

Being among the youngest within a school class is linked to disadvantages in various educational and mental health domains. This study aimed to investigate whether preterm born infants are particularly vulnerable to relative age effects on mental health, not previously studied.

METHODS

We used registry data on all Norwegians born between 1989 and 1998 to compare prescription status for psychostimulants, antidepressants, hypnotics, anxiolytics, and antipsychotics per year from age 10 to 23 years (2004-2016) between exposure groups with different time of birth in the year (relative age) and different gestational age (preterm versus term).

RESULTS

Of 488 470 individuals, 29 657 (6,1%) were born preterm. For term born in November/December, the adjusted odds ratio (aORs) for psychostimulant prescription compared with peers born in January/February was 1.80 (95% confidence interval [CI], 1.69-1.91) at ages 10 to 14 years, and 1.17 (95% CI, 1.08-1.27) at ages 20 to 23 years. Within preterm born, the corresponding results were 1.39 (95% CI, 1.13-1.69) and 1.34 (95% CI, 1,00-1.78) at ages 10 through 14 and 20 through 23 years, respectively.

CONCLUSIONS

Being relatively young within the school group was associated with increased psychostimulant prescription in the preterm as well as the term population. In contrast to term peers, the relative age effect for psychostimulant prescription seemed to persist to young adulthood for the preterm population. The results suggest that preterm individuals are vulnerable to long-term effects of relative immaturity and that they require careful consideration from both health care professionals and the school system.

Difficulties in Managing Children's Learning among Caregivers of Children with Attention-Deficit/Hyperactivity Disorder during the COVID-19 Pandemic in Taiwan: Association with Worsened Behavioral and Emotional Symptoms

School closures during the COVID-19 pandemic have interfered with children's learning. The aim of this study was to investigate the difficulties in managing children's learning at home and attending afterschool learning programs and their related factors among caregivers of children with attention-deficit/hyperactivity disorder (ADHD) during the COVID-19 pandemic. In total, 252 caregivers of children with ADHD completed a questionnaire collecting difficulties in managing children's learning, parenting styles, children's worsened symptoms of ADHD, oppositional defiant disorder (ODD) and emotion, and increased Internet use. Multivariate logistic regression models were used to examine the factors related to caregiver difficulties in managing children's learning and children's worsened ADHD, ODD, and emotional symptoms. In total, 85.3% of the caregivers had difficulty in asking their children to learn at home; 28.2% had difficulty in taking children to afterschool learning programs. Children's worsened anger was significantly associated with higher caregiver difficulty in asking children to learn at home, whereas parental overprotection was significantly associated with lower caregiver difficulty in asking children to learn at home. Worsened hyperactivity and opposition were significantly associated with higher caregiver difficulty in taking children to attend afterschool learning programs. Interventions for enhancing caregivers' skills to manage children's learning and children's behavioral and emotional symptoms should take the related factors found in this study into consideration.

Children's Relative Age and Medicine Treatment for Attention-Deficit/Hyperactivity Disorder Across Australian Jurisdictions with Different School Enrolment Policies

Background: Children who are relatively young for their school grade are more likely to receive treatment for attention-deficit/hyperactivity disorder (ADHD). It is unclear whether the phenomenon also exists across Australia or is impacted by the school enrolment policy in place. Objective: We evaluated the association between children's relative age and initiation of ADHD medicines across Australian jurisdictions with different school enrolment policies and rates of delayed school entry. Methods: We used Australia-wide dispensing data for a 15% random sample of children 4-9 years of age in 2013-2017 to create a nationwide cohort. Due to high rates of delayed school entry in New South Wales (NSW), we used linked prescribing and education data for a cohort of NSW residents starting school in 2009 and 2012. We estimated incidence rate ratios (IRRs) for ADHD medicine across children's birth month, sex, and jurisdiction. We used asthma medicines as a negative control. Results: For girls, we observed a relative age effect in three out of five jurisdictions, with an IRR ranging from 1.3 to 2.8, comparing the youngest versus oldest birth month thirds. We observed more modest effects among boys, ranging from null to 1.5-fold. In NSW, the relatively youngest boys were less likely to initiate stimulant medicines than the oldest (IRR = 0.5, 95% confidence interval 0.29-0.78). We did not observe a relative age effect for initiation of asthma medicines. Conclusions: In jurisdictions with low rates of delayed entry, relatively young children were more likely to initiate ADHD medicines than their older classmates. We observed the inverse association in NSW where delayed entry was highest, likely reflecting the characteristics and needs of children who delay school entry for 1 year and become the oldest children in the grade. Increased awareness around children's maturity differences and school readiness may enhance appropriate diagnosis and treatment of ADHD.

Klerman's "credo" reconsidered: neo-Kraepelinianism, Spitzer's views, and what we can learn from the past

In 1978, G. Klerman published an essay in which he named the then-nascent "neo-Kraepelinian" movement and formulated a "credo" of nine propositions expressing the movement's essential claims and aspirations. Klerman's essay appeared on the eve of the triumph of neo-Kraepelinian ideas in the DSM-III. However, this diagnostic system has subsequently come under attack, opening the way for competing proposals for the future of psychiatric nosology. To better understand what is at stake, in this paper I provide a close reading and consideration of Klerman's credo in light of the past forty years of research and reflection. The credo is placed in the context of two equally seminal publications in the same year, one by S. Guze, the leading neo-Kraepelinian theorist, and the other by R. Spitzer and J. Endicott, defining mental disorder. The divergences between Spitzer and standard neo-Kraepelinianism are highlighted and argued to be much more important than is generally realized. The analysis of Klerman's credo is also argued to have implications for how to satisfactorily resolve the current nosological ferment in psychiatry. In addition to issues such as creating descriptive syndromal diagnostic criteria, overthrowing psychoanalytic dominance of psychiatry, and making psychiatry more scientific, neo-Kraepelinians were deeply concerned with the conceptual issue of the nature of mental disorder and the defense of psychiatry's medical legitimacy in response to antipsychiatric criticisms. These issues cannot be ignored, and I argue that proposals currently on offer to replace the neo-Kraepelinian system, especially popular proposals to replace it with dimensional measures, fail to adequately address them.

Editorial: Youngest Kids in Class and Their Long-term Outcomes

In this issue of the JAACAP, Kuntsi et al.⁷ reports from the Swedish national registers to analyze the outcomes of almost 300,000 individuals who were relatively young or relatively old in class (ie, born in the 2 months before and after the national cut-off for school entrance in Sweden). Four events were measured between 15 and 23 years of age: low educational achievement, a conviction of any crime, substance use disorder, and depression. As predicted, young relative age was a risk factor for ADHD (with an odds ratio of 1.7), which in turn was a risk factor for all 4 outcomes considered (with odds ratios of 3.5-5.2). The novelty of their analyses, however, was to evaluate the additive effects of relative young age beyond ADHD on negative long-term outcomes. For the first time, Kuntsi et al.⁷ demonstrated that children with ADHD who are the youngest in their class are at increased risk for lower educational achievement and receiving a diagnosis of substance use disorder when compared to children with ADHD who are the oldest in their class.

The Combined Effects of Young Relative Age and Attention-Deficit/Hyperactivity Disorder on Negative Long-term Outcomes

OBJECTIVE

Young relative age (ie, being among the youngest in a school class) and attention-deficit/hyperactivity disorder (ADHD) are both potential risk factors for adverse long-term outcomes. Young relative age also increases the risk of ADHD diagnosis. Using data from Swedish national registers, we investigate the independent and joint long-term effects of young relative age and ADHD on educational achievement, substance use disorder (SUD), criminality, and depression.

METHOD

We identified a national cohort of individuals with young relative age (born November-December) and a comparison group with old relative age (born January-February). Of the total sample of 297,840 individuals, 6,528 individuals had a diagnosis of ADHD in childhood. The 4 outcomes were measured at ages 15 to 23 years. We examined main, additive, and interactive effects of young relative age and ADHD on long-term outcomes.

RESULTS

In the individuals without ADHD, young relative age was associated with increased risk of depression (odds ratio [OR] = 1.14 [95% CI =1.09-1.20]), SUD (OR = 1.14 [1.09-1.20]), and low educational achievement (OR = 1.17 [1.14-1.20]), but not criminality (OR = 1.00 [0.98-1.03]). In the individuals with ADHD, young relative age was associated with increased risk of SUD (OR = 1.23 [1.01-1.50]) and low educational achievement (OR = 1.12 [1.00-0.26]; CI included 1), but not depression or criminality (OR = 0.88 [0.73-1.07] and OR = 0.89 [0.79-1.01], respectively). An interaction emerged between young relative age and ADHD for depression (OR = 0.78 [0.64-0.95]).

CONCLUSION

We observed relative age effects that add to the evidence supporting a more flexible approach to school starting age and that emphasize the importance of careful age-match comparisons during assessment of childhood ADHD symptoms.

Respect for Persons in the Psychiatric Treatment of Children and Adolescents

Child and adolescent psychiatry involves simultaneously balancing duties to various vulnerable parties. Balancing autonomy and protection for adolescents is complex; state laws governing these situations often add confusion. Common prescribing patterns in child psychiatry lack robust evidence, and utilization of stimulants, atypical antipsychotics, and polypharmacy has skyrocketed. Significant concerns about distributive justice arise from alarming patterns in psychiatric treatment of vulnerable populations, like those affected by poverty, racism, adverse childhood experiences, and certain legal statuses. Principles of justice and respect for persons support the need for safe, adequate, and appropriate psychiatric treatment, including psychosocial interventions and resources, for all children.

The assignment and distribution of the dyslexia label: Using the UK Millennium Cohort Study to investigate the socio-demographic predictors of the dyslexia label in England and Wales

The prevalence of dyslexia identification has increased significantly over the last two decades. Yet there is debate over whether there are distinct biological and cognitive differences between those with literacy difficulties and the subgroup of people identified as dyslexic. This is the first paper that provides evidence for this ongoing debate by investigating the socio-demographic factors, outside biology and cognition, that predict whether a child is identified as dyslexic in the UK. Using secondary data from the UK's Millennium Cohort Study, this paper examines the socio-demographic factors that predict whether a child's teacher identifies them as dyslexic at age 11. Gender, season of birth, socio-economic class and parental income are found to be significant predictors of the dyslexia label. Therefore, factors seemingly unrelated to the clinical aspects of dyslexia influence whether a child is identified as dyslexic in England and Wales. This suggests that label may not be evenly distributed across a population; furthermore, it may also indicate that resources for support may not be fairly allocated. The findings further support the argument that a 'dyslexic sub-group' within poor readers is created due to the impact of environmental factors. The results from this national-scale study thus questions the reliability, validity and moral integrity of the allocation of the dyslexia label across current education systems in the UK.

Relative age and specific learning disorder diagnoses: A Finnish population-based cohort study

Background

Being among the youngest in class has previously been associated with attention-deficit/hyperactivity disorder (ADHD) and academic disadvantage, but the relative age effect on learning disorders is less well understood. This study examined whether relatively young children are more likely to be diagnosed with specific learning disorders than their older peers.

Methods

The setting included all 388,650 children born singleton in Finland from 1996 to 2002. Cases diagnosed with specific learning disorders in specialized health care by the age of 10 were identified from national registers. Cumulative incidences of specific learning disorders and the corresponding incidence rate ratios (IRRs) and 95% confidence intervals (CIs) were calculated for each birth month compared to January.

Results

During follow-up, 3162 (0.8% of 388,650) children were diagnosed with a specific learning disorder. Children born in December displayed higher cumulative incidences for specific learning disorders than children born in January (IRR: 1.77, 95% CI: 1.50-2.11). The findings were similar for girls (IRR: 2.01, 1.44-2.83) and boys (IRR: 1.70, 1.39-2.08). ADHD did not explain the association, as the IRR for the youngest children with specific learning disorders and ADHD was 1.59 (1.13-2.26) compared to those without ADHD (IRR: 1.84, 1.51-2.24).

Conclusions

Relatively younger children in Finnish schools were more likely to be diagnosed with a specific learning disorder by the age of 10. Increased awareness of how relative age differences affect the likelihood for children to be diagnosed with specific learning disorders is needed among parents, clinicians, and teachers.

Impact of attention deficit hyperactivity disorder and gender differences on academic and social difficulties among adolescents in Qatari Schools

Background: To evaluate the social and academic impact of adolescents with Attention Deficit Hyperactivity Disorder (ADHD) and gender differences compared with their non-ADHD peers.

Methods: A cross-sectional descriptive study using a standardized rating scale of teacher observations was conducted in the schools of Qatar from 7^th to 12^th grades. Teachers completed Swanson, Nolan, and Pelham (SNAP-IV) rating scale questionnaires for the ADHD core symptoms together with nine questions to evaluate the academic and social difficulties in all participants.

Results: A total of 1775 students (mean age: 15 ± 1.5 years; boys/girls: 717/1058) were included in this study. Based on the SNAP-IV rating scale, 150 students were showing core symptoms of ADHD and classified as having ADHD (8.5%; boys/girls; 93/57) and 1625 students as non-ADHD peers (91.5%; boys/girls; 624/1001). Prevalence of ADHD among adolescent students is 8.5%, and it varied significantly between genders with 13% of boys and 5.4% of girls affected by this disorder. Adolescents with ADHD had more academic and social difficulties than their non-ADHD peers, the boys more so than the girls. Boys with inattentive subtype of ADHD had more academic difficulties than girls, while girls had more social difficulties than boys.

Conclusion: The results of this study revealed that ADHD among adolescents is substantially associated with academic and social difficulties in the school environment. Gender differences among students with ADHD should be considered in the school and clinical environment.

Children's Relative Age and ADHD Medication Use: A Finnish Population-Based Study

OBJECTIVES

The youngest children in a classroom are at increased risk of being medicated for attention-deficit/hyperactivity disorder (ADHD). We examined the association between children's birth month and ADHD medication rates in Finland.

METHODS

Using a population-based study, we analyzed ADHD medication use among children born in 2005 to 2007. Cases (n = 7054) were identified from the first purchase of medication for ADHD. Cox proportional hazard models and hazard ratios (HRs) were examined by birth month and sex. Finnish children start first grade in the year of their seventh birthday. The cutoff date is December 31.

RESULTS

Risk of ADHD medication use increased throughout the year by birth month (ie, January through April to May through August to September through December). Among boys born in September to December, the association remained stable across cohorts (HR: 1.3; 95% confidence interval [CI]: 1.1-1.5). Among girls born in September to December, the HR in the 2005 cohort was 1.4 (95% CI: 1.1-1.8), whereas in the 2007 cohort it was 1.7 (95% CI: 1.3-2.2). In a restricted follow-up, which ended at the end of the year of the children's eighth birthday, the HRs for boys and girls born in September to December 2007 were 1.5 (95% CI: 1.3-1.7) and 2.0 (95% CI: 1.5-2.8), respectively.

CONCLUSIONS

Relative immaturity increases the likelihood of ADHD medication use in Finland. The association was more pronounced during the first school years. Increased awareness of this association is needed among clinicians and teachers.

Relative Age and Attention-Deficit/Hyperactivity Disorder: Data From Three Epidemiological Cohorts and a Meta-analysis

OBJECTIVE

To investigate the effect of relatively younger age on attention-deficit/hyperactivity disorder (ADHD) symptoms and diagnosis through three population-based cohorts and a meta-analysis.

METHOD

This study included participants of three community-based cohorts in Brazil: 1993 Pelotas Cohort (N = 5,249), 2004 Pelotas Cohort (N = 4,231), and Brazilian High-Risk Study for Psychiatric Disorders (HRC study) (N = 2,511). We analyzed the effect of relatively younger age on ADHD symptoms and diagnosis. For the meta-analysis, we searched MEDLINE, PsycINFO, and Web of Science from inception through December 25, 2018. We selected studies that reported measures of association between relative immaturity and an ADHD diagnosis. We followed the Meta-analysis Of Observational Studies in Epidemiology guidelines. The protocol for meta-analysis is available on PROSPERO (CRD42018099966).

RESULTS

In the meta-analysis, we identified 1,799 potentially eligible records, from which 25 studies including 8,076,570 subjects (164,049 ADHD cases) were analyzed with their effect estimates. The summarized relative risk of an ADHD diagnosis was 1.34 (95% CI, 1.26-1.43, p < .001) for children born in the first 4 months of the school year (relatively younger). Heterogeneity was high (I² = 96.7%). Relative younger age was associated with higher levels of ADHD symptoms in the 1993 Pelotas Cohort (p = .003), 2004 Pelotas Cohort (p = .046), and HRC study (p = .010).

CONCLUSION

Children and adolescents who are relatively younger compared with their classmates have a higher risk of receiving an ADHD diagnosis. Clinicians should consider the developmental level of young children when evaluating ADHD symptoms.

Association between exposure to polycyclic aromatic hydrocarbons and attention deficit hyperactivity disorder in children: a systematic review and meta-analysis

Some studies have shown that exposure to polycyclic aromatic hydrocarbons (PAHs) is a dangerous factor for attention deficit hyperactivity disorder (ADHD). This systematic review and meta-analysis aimed to clarify this relationship, and to collect and analyze all the relevant evidences in published reports of epidemiologic studies. PubMed, Science Direct, Web of Science, Scopus, and Google Scholar databases were searched through September 31, 2018. The study quality was evaluated using the Newcastle-Ottawa Scale. Moreover, fixed- and random-effect models were used. The data in this meta-analysis were presented as adjusted odds ratio (AOR). From 959 articles, six articles were included in the systematic review, and for meta-analysis, one study (that was not AOR) was excluded. The participants included in the studies were 2799 with the age range of 5-15 years old, and 93.6% were living in America. Four of the studies were placed in one group, due to having a common author (Perera). Moreover, a significant association was found between PAH exposure and ADHD in these studies (odds ratio = 2.57, 95% CI = 1.75-3.78); however, in all studies, there was no significant association between PAH exposure and ADHD for children (overall odds ratio = 1.99, 95% CI = 0.96-4.11) with low heterogeneity (I² = 28.73%; P value < 0.001). This study provided a systematic review and meta-analytic evidence for the association between PAH exposure and ADHD by a small number of studies. Further research study can be conducted in various countries. Graphical Abstract.

What Differentiates Children with ADHD Symptoms Who Do and Do Not Receive a Formal Diagnosis? Results from a Prospective Longitudinal Cohort Study

ADHD diagnoses are increasing worldwide, in patterns involving both overdiagnosis of some groups and underdiagnosis of others. The current study uses data from a national longitudinal study of Irish children (N = 8568) to examine the sociodemographic, clinical and psychological variables that differentiate children with high hyperactivity/inattention symptoms, who had and had not received a diagnosis of ADHD. Analysis identified no significant differences in the demographic characteristics or socio-emotional wellbeing of 9-year-olds with hyperactivity/inattention who had and who had not received a diagnosis of ADHD. However, by age 13, those who had held a diagnosis at 9 years showed more emotional and peer relationship problems, worse prosocial behaviour, and poorer self-concept. Further research is required to clarify the developmental pathways responsible for these effects.

Attention deficit hyperactivity disorder late birthdate effect common in both high and low prescribing international jurisdictions: a systematic review

BACKGROUND

Multiple studies have found that the youngest children in a classroom are at elevated risk of being diagnosed with, or medicated for, ADHD. This systematic review was conducted to investigate whether this late birthdate effect is the norm and whether the strength of effect is related to the absolute risk of being diagnosed/medicated.

METHODS

A literature search of the PubMed and ERIC databases and snowball and grey literature searching were conducted.

RESULTS

A total of 19 studies in 13 countries covering over 15.4 million children investigating this relationship were identified. Three other studies exploring related topics were identified. The diversity of methodologies prevented a meta-analysis. Instead a systematic review of the 22 studies was conducted. A total of 17 of the 19 studies found that the youngest children in a school year were considerably more likely to be diagnosed and/or medicated than their older classmates. Two Danish studies found either a weak or no late birth date effect. There was no consistent relationship between per-capita diagnosis or medication rates and the strength of the relative age effect, with strong effects reported in most jurisdictions with comparatively low rates.

CONCLUSIONS

It is the norm internationally for the youngest children in a classroom to be at increased risk of being medicated for ADHD, even in jurisdictions with relatively low prescribing rates. A lack of a strong effect in Denmark may be accounted for by the common practice of academic 'redshirting', where children judged by parents as immature have a delayed school start. Redshirting may prevent and/or disguise late birthdate effects and further research is warranted. The evidence of strong late birthdate effects in jurisdictions with comparatively low diagnosis/medication rates challenges the notion that low rates indicate sound diagnostic practices.

Relative age and ADHD symptoms, diagnosis and medication: a systematic review

There is a growing international literature investigating the relationship between attention-deficit/hyperactivity disorder (ADHD) and younger relative age within the school year, but results have been mixed. There are no published systematic reviews on this topic. This study aimed to systematically review the published studies on the relative age effect in ADHD. Systematic database searches of: Medline, Embase, PsycINFO, Web of Science, ERIC, Psychology and Behavioral Sciences Collection and The Cochrane Library were conducted. Studies were selected which investigated the relative age effect in ADHD in children and adolescents. Twenty papers were included in the review. Sixteen (of 20) papers reported a significantly higher proportion of relatively younger children being diagnosed with ADHD and/or receiving medication for this. Meta-analyses involving 17 of these 20 papers revealed a modest relative age effect in countries with higher prescribing rates, risk ratio = 1.27 (95% CI 1.19-1.35) for receipt of medication. The relative age effect is well demonstrated in countries with known higher prescribing rates. Amongst other countries, there is also increasing evidence for the relative age effect, however, there is high heterogeneity amongst studies. Further research is needed to understand the possible reasons under-pinning the relative age effect and to inform attempts to reduce it.

Young age at school entry and attention-deficit hyperactivity disorder-related symptoms during primary school: results of a prospective cohort study conducted at German Rudolf Steiner Schools

OBJECTIVES

Young age at school entry (ASE) for students has been related to their impaired mental health in higher grades. To avoid the negative health consequences of young ASE, preschool examinations and individual school entry deferral for young children are routinely performed by some school authorities. We aimed to investigate whether ASE was associated with attention-deficit hyperactivity disorder (ADHD)-related symptoms in pupils attending schools using a selective school enrolment procedure.

DESIGN

Prospective open cohort study with baseline assessments at school entry and two follow-ups in the second and fourth grades.

SETTING

Up to 128 Rudolf Steiner Schools (Waldorf Schools) located within Germany.

PARTICIPANTS

Of the 3079 children from whom data were gathered in the second or fourth grade, 2671 children born between 1 July 2001 and 31 October 2002 (age at baseline: mean 6.7, min 5.91, max 7.24 years, 50% girls) were selected for analysis to avoid bias introduced by individuals at the edges of the ASE distribution.

MAIN OUTCOME MEASURES

ADHD-related symptoms were assessed at school entry and second and fourth grades by parent-reported and teacher-reported versions of the Strengths and Difficulties Questionnaire (Hyperactivity-Inattention Subscale).

RESULTS

The agreement between parent-reported and teacher-reported symptoms was poor (intra-class correlation: 0.41 and 0.44 in second and fourth grade assessments, respectively). Regarding teacher reports, ASE was negatively associated with ADHD-related symptoms in the second grade (regression coefficient β=-0.66 per year, P=0.0006) and fourth grade (β=-0.56, P=0.0014). Associations remained after adjusting for potential confounders and pre-existing symptoms at baseline. Regarding parent reports, associations were markedly weaker in both grades (second grade: β=-0.22, P=0.12; fourth grade: β=-0.09, P=0.48).

CONCLUSIONS

Using a prospective study design and comprehensive adjustment for confounding and baseline symptoms, we confirmed prior evidence of the association between young ASE and teacher-reported ADHD symptoms in primary school.

Timing of White Matter Development Determines Cognitive Abilities at School Entry but Not in Late Adolescence

The primary aim of this study was to investigate to what degree the age-related white matter development, here called "brain age", is associated with working memory (WM) and numeric abilities in 6-year-old children. We measured white matter development using diffusion tensor imaging to calculate fractional anisotropy (FA). A "brain age" model was created using multivariate statistics, which described association between FA and age in a sample of 6- to 20-year-old children. This age model was then applied to predict "brain age" in a second sample of 6-year-old children. The predicted brain age correlated with WM performance and numerical ability (NA) (P < 0.01, P < 0.05) in the 6-year-old children. More than 50% of the stable variance in WM performance was explained. We found that in children older than 13 years of age, this association between brain age and WM was no longer significant (P > 0.5). The results bear theoretical implications as they suggest that the variability in individual developmental timing strongly affects WM and NA at school start but badly predicts adolescent cognitive functioning. Furthermore, it bears practical implications as one may differentiate maturation lags from persistent low cognitive abilities in school children, complementing cognitive tests.

ADHD: a critical update for educational professionals

A medical approach towards behavioural problems could make professionals without a medical background, like teachers and other educational professionals feel inapt. In this article, we raise six scientifically grounded considerations regarding ADHD, currently the most prevalent childhood psychiatric diagnosis. These "need to knows" show just how misguided and potentially stigmatizing current conceptualizations of unruly behaviour have become. Some examples are given of how teachers are misinformed, and alternative ways of reporting about neuropsychological research are suggested. A reinvigorated conceptual understanding of ADHD could help educational institutions to avoid the expensive outsourcing of behavioural problems that could also-and justifiably better-be framed as part of education's primary mission of professionalized socialization.

Relative age within the school year and diagnosis of attention-deficit hyperactivity disorder: a nationwide population-based study

BACKGROUND

Findings are mixed on the relationship between attention-deficit hyperactivity disorder (ADHD) and younger relative age in the school year. We aimed to investigate whether relative age is associated with ADHD diagnosis in a country where prescribing rates are low and whether any such association has changed over time or relates to comorbid disorders (eg, conduct disorder [CD], oppositional defiant disorder [ODD], or learning disorder [LD]).

METHODS

We used nationwide population-based registers to identify all Finnish children born between Jan 1, 1991, and Dec 31, 2004, who were diagnosed with ADHD from age 7 years onwards (age of starting school). We calculated incidence ratios to assess the inter-relations between relative age within the school year, age at ADHD diagnosis, and year of diagnosis (1998-2003 vs 2004-11).

FINDINGS

Between Jan 1, 1998, and Dec 31, 2011, 6136 children with ADHD were identified. Compared with the oldest children in the school year (ie, those born between January and April), the cumulative incidence of an ADHD diagnosis was greatest for the youngest children (ie, those born between September and December); for boys the incidence ratio was 1·26 (95% CI 1·18-1·35; p<0·0001) and for girls it was 1·31 (1·12-1·54; p=0·0007). The association between relative age and age at ADHD diagnosis reflected children diagnosed before age 10 years, and the strength of this association increased during recent years (2004-11). Thus, compared with children born between January and April, for those born between May and August, the ADHD incidence ratio was 1·37 (95% CI 1·24-1·53; p<0·0001) and for those born between September and December, the incidence ratio was 1·64 (1·48-1·81; p<0·0001). The relative age effect was not accounted for by comorbid disorders such as CD, ODD, or LD.

INTERPRETATION

In a health service system with low prescribing rates for ADHD, a younger relative age is associated with an increased likelihood of receiving a clinical diagnosis of ADHD. This effect has increased in recent years. Teachers, parents, and clinicians should take relative age into account when considering the possibility of ADHD in a child or encountering a child with a pre-existing diagnosis.

FUNDING

Academy of Finland, Finnish Medical Foundation, Orion Pharma Foundation, Finnish Cultural Foundation.

Uncovering exposures responsible for birth season - disease effects: a global study

Objective

Birth month and climate impact lifetime disease risk, while the underlying exposures remain largely elusive. We seek to uncover distal risk factors underlying these relationships by probing the relationship between global exposure variance and disease risk variance by birth season.

Material and Methods

This study utilizes electronic health record data from 6 sites representing 10.5 million individuals in 3 countries (United States, South Korea, and Taiwan). We obtained birth month–disease risk curves from each site in a case-control manner. Next, we correlated each birth month–disease risk curve with each exposure. A meta-analysis was then performed of correlations across sites. This allowed us to identify the most significant birth month–exposure relationships supported by all 6 sites while adjusting for multiplicity. We also successfully distinguish relative age effects (a cultural effect) from environmental exposures.

Results

Attention deficit hyperactivity disorder was the only identified relative age association. Our methods identified several culprit exposures that correspond well with the literature in the field. These include a link between first-trimester exposure to carbon monoxide and increased risk of depressive disorder (R = 0.725, confidence interval [95% CI], 0.529-0.847), first-trimester exposure to fine air particulates and increased risk of atrial fibrillation (R = 0.564, 95% CI, 0.363-0.715), and decreased exposure to sunlight during the third trimester and increased risk of type 2 diabetes mellitus (R = −0.816, 95% CI, −0.5767, −0.929).

Conclusion

A global study of birth month–disease relationships reveals distal risk factors involved in causal biological pathways that underlie them.

ADHD treatment and diagnosis in relation to children's birth month: Nationwide cohort study from Norway

BACKGROUND

Studies from several countries have reported that children youngest in grade are at higher risk of attention-deficit/hyperactivity disorder (ADHD) diagnosis and treatment. Norwegian children start school the year they turn six, making children born in December youngest in their grade. We used data on medication, specialist healthcare diagnoses, and primary healthcare diagnoses from national registers to investigate associations between birth month and ADHD.

METHODS

All children born in Norway between 1998 and 2006 ( N=509,827) were followed from age six until 31 December 2014. We estimated hazard ratios for ADHD medication and diagnoses by birth month in Cox proportional-hazards models. We compared risk among siblings to control for potentially confounding socioeconomic factors, and assessed risk of receiving ADHD medication by birth month while attending different grades in cross-sectional time-series analyses.

RESULTS

At end of follow-up, 5.3% of boys born in October-December had received ADHD medication, compared with 3.7% of boys born in January-March. Corresponding numbers for girls were 2.2% and 1.3%, respectively. The adjusted hazard ratio for ADHD medication for children born in October-December (reference: January-March) was 1.4 (95% confidence interval: 1.4-1.5) for boys and 1.8 (1.7-2.0) for girls. Analyses with diagnoses as outcome showed consistent results, and analyses restricted to siblings within the study population also supported the findings. Analysis by grade revealed an increased risk for children born late in the year from grade 3 onwards, with most marked differences in higher grades.

CONCLUSIONS

Children youngest in grade had the highest risk of receiving ADHD treatment. Differences were most marked among older children.

Overdiagnosis of mental disorders in children and adolescents (in developed countries)

During the past 50 years, health insurance providers and national registers of mental health regularly report significant increases in the number of mental disorder diagnoses in children and adolescents. However, epidemiological studies show mixed effects of time trends of prevalence of mental disorders. Overdiagnosis in clinical practice rather than an actual increase is assumed to be the cause for this situation. We conducted a systematic literature search on the topic of overdiagnosis of mental disorders in children and adolescents. Most reviewed studies suggest that misdiagnosis does occur; however, only one study was able to examine overdiagnosis in child and adolescent mental disorders from a methodological point-of-view. This study found significant evidence of overdiagnosis of attention-deficit/hyperactivity disorder. In the second part of this paper, we summarize findings concerning diagnostician, informant and child/adolescent characteristics, as well as factors concerning diagnostic criteria and the health care system that can lead to mistakes in the routine diagnostic process resulting in misdiagnoses. These include the use of heuristics instead of data-based decisions by diagnosticians, misleading information by caregivers, ambiguity in symptom description relating to classification systems, as well as constraints in most health systems to assign a diagnosis in order to approve and reimburse treatment. To avoid misdiagnosis, standardized procedures as well as continued education of diagnosticians working with children and adolescents suffering from a mental disorder are needed.

Association Between Age of Beginning Primary School and Attention Deficit Hyperactivity Disorder

OBJECTIVE

In April 2012, the Turkish national education system was modified, and the compulsory school age of entry (first grade) was redefined as a minimum of 60 months and a maximum of 66 months (replacing the former minimum criterion of 72 months). In this study, we hypothesized that students starting school before 72 months (the previous age standard for the first grade) may experience (1) a greater number of symptoms of attention deficit hyperactivity disorder (ADHD) and (2) lower functioning in social, behavioral, and academic domains.

METHOD

We performed a cross-sectional community-based study in the first and second grades of all primary schools (4356 students) located in the Kadıköy county of Istanbul, Turkey. Teachers completed Swanson, Nolan, and Pelham version IV and Conners' Teacher's report forms for symptoms of ADHD, the Perceived Competence Scale for functioning, and a sociodemographic questionnaire.

RESULTS

Among first graders, the group that began primary school before the age of 72 months had a higher ADHD prevalence than both of the groups that began primary school between the ages of 72 to 77 months and 78 to 83 months (p < .001 for both groups). ADHD symptoms diminished and academic, social, and behavioral functioning improved with age for the first and second grade students.

CONCLUSION

The probability of displaying ADHD symptoms (and caseness) is greater among the "earlier" beginners, whereas the "conventional" classmates exhibited better academic, social, and behavioral functioning.

Clinical Correlates of Co-occurring Psychiatric and Autism Spectrum Disorder (ASD) Symptom-Induced Impairment in Children with ASD

Although psychiatric symptom severity and impairment are overlapping but nevertheless distinct illness parameters, little research has examined whether variables found to be associated with the severity are also correlated with symptom-induced impairment. Parents and teachers completed ratings of symptom-induced impairment for DSM-IV-referenced syndromes, and parents completed a background questionnaire for a consecutively referred sample of primarily male (81%) 6-to-12 year olds with autism spectrum disorder (ASD) (N = 221). Some clinical correlates (e.g., IQ < 70, maternal level of education, pregnancy complications, current use of psychotropic medication, season of birth) were associated with impairment for several disorders, whereas others were correlated with only a few syndromes (e.g., gender, co-morbid medical conditions) or were not related to impairment in any disorder (e.g., family psychopathology). There was little convergence in findings for parents' versus teachers' ratings. Some clinical correlates (e.g., season of birth, current psychotropic medication, maternal education) were unique predictors of three or more disorders. Pregnancy complications were uniquely associated with social anxiety and schizoid personality symptom-induced impairment. IQ was a unique predictor of schizophrenia, ASD, oppositional defiant disorder symptom-induced impairment. Children whose mothers had relatively fewer years of education had greater odds for symptom-induced impairment in social anxiety, depression, aggression, and mania and greater number of impairing conditions. Season of birth was the most robust correlate of symptom-induced impairment as rated by teachers but not by parents. Children born in fall evidenced higher rates of co-occurring psychiatric and ASD symptom-induced impairment and total number of impairing conditions. Many variables previously linked with symptom severity are also correlated with impairment.

Relative Immaturity in Childhood and Attention-Deficit/Hyperactivity Disorder Symptoms From Childhood to Early Adulthood: Exploring Genetic and Environmental Overlap Across Development

OBJECTIVE

Attention-deficit/hyperactivity disorder (ADHD) has been linked to immaturity relative to peers in childhood, yet it is unclear how such immaturity is associated with ADHD across development. This longitudinal twin study examined the genetic and environmental contributions to the association between parents' perception of their child's immaturity relative to peers (RI) in childhood and ADHD symptoms across development.

METHOD

1,302 twin pairs from the Swedish Twin Study of Child and Adolescent Development were followed prospectively from childhood to early adulthood. Parent ratings of RI were collected at 8 to 9 years and parent and self-ratings of ADHD symptoms were collected at 8 to 9, 13 to 14, 16 to 17, and 19 to 20 years using the Child Behavior Checklist Attention Problems scale. In addition, ADHD symptoms corresponding to DSM criteria were used for sensitivity analysis. Analyses were conducted using longitudinal structural equation modeling with multiple raters.

RESULTS

RI-related etiologic factors, predominantly influenced by genes, explained 10-14% of the variance in ADHD symptoms from 8 to 9 up to 16 to 17 years. The influence of these RI-related factors on ADHD symptoms attenuated to 4% by 19 to 20 years of age. The remaining variance in ADHD symptoms was primarily explained by genetic factors independent of RI, which remained relatively stable across development, explaining 19% to 30% of the variance in ADHD symptoms from 13 to 14 up to 19 to 20 years.

CONCLUSION

The results show that RI is significantly associated with ADHD symptoms, particularly during childhood and adolescence, and that the association is primarily explained by a shared genetic liability. Nevertheless, the magnitude of associations across development was modest, highlighting that RI is merely one aspect contributing to the complex etiology of ADHD symptoms.

Influence of Relative Age on Diagnosis and Treatment of Attention-Deficit Hyperactivity Disorder in Taiwanese Children

OBJECTIVE

To determine the potential influence of relative age on the diagnosis and treatment of attention-deficit hyperactivity disorder (ADHD), especially in reference to an Asian country.

STUDY DESIGN

A total of 378 881 subjects aged 4-17 years during the study period (September 1, 1997 to August 31, 2011) were enrolled in our study from the Taiwan National Health Insurance Research Database. Logistic regression analysis was used to examine the likelihood of receiving ADHD diagnosis and treatment for those who were born in August (the youngest) compared with those who were born in September (the oldest).

RESULTS

Both boys and girls born in August had a higher risk of being diagnosed with ADHD (OR 1.63, 95% CI 1.45-1.84; OR 1.71, 95% CI 1.36-2.15) and receiving ADHD medication (OR 1.76, 95% CI 1.53-2.02; OR 1.65, 95% CI 1.26-2.18) than those born in September. Sensitivity tests conducted over different periods revealed consistent findings.

CONCLUSIONS

Relative age, as an indicator of neurocognitive maturity, is crucial in the risk of being diagnosed with ADHD and receiving ADHD medication among children and adolescents. Our findings emphasize the importance of considering the age of a child within a grade when diagnosing ADHD and prescribing medication for treating ADHD.

Stimulant use for ADHD and relative age in class among children in Israel

BACKGROUND

Diagnosis of children with attention-deficit/hyperactivity disorder (ADHD) is increasing. The present study sought to identify characteristics and medication treatment patterns of children with ADHD and compare them by relative age in class, sex, ethnicity, family size, sibling order, and other socioeconomic status, as well as find trends in disparity of pharmacotherapy.

METHODS

This study was based on data from 1 013 149 Clalit Health Services members aged 6-17 years during 2006-2011. Centrally acting sympathomimetic drug purchases were compared according to children's estimated relative age in class; youngest third (born August to November), middle third (born April to July), and oldest third (born December to March). Treatment trends were determined and compared according to sociodemographic and family-related factors.

RESULTS

The overall prevalence of stimulant use in the population was 2.6% in 2006 and 4.9% in 2011. The annual incidence of stimulant use increased from 0.75% to 1.36%, rising more sharply among children in the older age groups (≥12) than among younger ones. Moreover, the youngest third of children in class was more likely to use medication than the oldest third (risk ratio (RR) 1.17, confidence interval (CI) 1.12-1.23) or the middle third (RR 1.06, CI 1.01-1.11). Of the different ethnic sectors, incidence of stimulant use was highest among general Jewish (1.8% in 2011) and lowest among Arabs (0.37% in 2011).

CONCLUSIONS

The use of stimulant medication is growing among children in Israel. Although the overall use does not exceed the estimated prevalence of ADHD among children, the appropriateness of prescribing to the Israeli pediatric population, especially to the youngest children in class, may be questionable. Copyright © 2016 John Wiley & Sons, Ltd.

Diagnostic Issues and Controversies in DSM-5: Return of the False Positives Problem

The fifth revision of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) was the most controversial in the manual's history. This review selectively surveys some of the most important changes in DSM-5, including structural/organizational changes, modifications of diagnostic criteria, and newly introduced categories. It analyzes why these changes led to such heated controversies, which included objections to the revision's process, its goals, and the content of altered criteria and new categories. The central focus is on disputes concerning the false positives problem of setting a valid boundary between disorder and normal variation. Finally, this review highlights key problems and issues that currently remain unresolved and need to be addressed in the future, including systematically identifying false positive weaknesses in criteria, distinguishing risk from disorder, including context in diagnostic criteria, clarifying how to handle fuzzy boundaries, and improving the guidelines for "other specified" diagnosis.

What we do not know about ADHD… yet

PURPOSE OF REVIEW

This article provides an overview of current controversies in attention-deficit/hyperactivity disorder (ADHD) research, with an emphasis on recent findings that are directly relevant to clinical practice.

RECENT FINDINGS

Over the past few years, a number of studies have added key evidence to ongoing debates about the epidemiology, nosology, and treatment of ADHD. Although the causes of the rising prevalence of ADHD in the USA are still not fully understood, recent research suggests that environmental factors and changes to the diagnostic criteria may have played a role. In addition, there continues to be controversy surrounding the clinical diagnosis of ADHD and newly recognized, related conditions such as sluggish cognitive tempo. Recent studies have also challenged previous assumptions about the long-term effects of stimulant treatment on growth, academic achievement, and substance use. Moreover, although most complementary and alternative therapies for ADHD appear to be ineffective, there is emerging evidence supporting the value of fatty acid supplementation. Although these findings are promising, more research is needed on all fronts.

SUMMARY

Although research has shed light on unanswered questions about the epidemiology, nosology, and treatment of ADHD, much is still not known. An understanding of the most important current controversies in ADHD research may aid pediatricians in clinical decision making and allow them to counsel patients more effectively.

DSM-5, psychiatric epidemiology and the false positives problem

The revision effort leading to the publication of the fifth edition of the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders (DSM-5) was flawed in process, goals and outcome. The revision process suffered from lack of an adequate public record of the rationale for changes, thus shortchanging future scholarship. The goals, such as dimensionalising diagnosis, incorporating biomarkers and separating impairment from diagnosis, were ill-considered and mostly abandoned. However, DSM-5's greatest problem, and the target of the most vigorous and sustained criticism, was its failure to take seriously the false positives problem. By expanding diagnosis beyond plausible boundaries in ways inconsistent with DSM-5's own definition of disorder, DSM-5 threatened the validity of psychiatric research, including especially psychiatric epidemiology. I present four examples: increasing the symptom options while decreasing the diagnostic threshold for substance use disorder, elimination of the bereavement exclusion from major depression, allowing verbal arguments as evidence of intermittent explosive disorder and expanding attention-deficit/hyperactivity disorder to adults before addressing its manifest false positives problems.

Children's relative age in class and use of medication for ADHD: a Danish Nationwide Study

BACKGROUND

Previous studies from North America and Iceland have shown that the youngest children within a grade are up to twice as likely to be diagnosed and treated for attention-deficit/hyperactivity disorder (ADHD) compared with their older classmates. We aimed to investigate whether younger age in class is associated with an increased probability of being prescribed medication for ADHD among school-aged children in Denmark.

METHODS

We followed all Danish children between 2000 and 2012 from 1st through 6th grade (7-12 years). Among children who started school on their age-assigned grade level, we estimated the prevalence proportion ratio (PPR) of receiving ADHD medication between the youngest children in class (born in October-December) and the oldest in class (born in January-March), specified by grade level, calendar year and gender. As a sensitivity analysis, we added children not on their age-assigned grade level to the main calculations.

RESULTS

We identified 932,032 eligible children for the main analysis, of whom 17.3% were among the youngest and 26.5% among the oldest in class. In total, 1.2% eligible children filled at least one prescription for ADHD medication in 2000-2012. The average PPR over the study period was 1.08 (95% CI, 1.04-1.12) and remained stable across subgroups and sensitivity analyses. Overall, 40% of children born October-December had entered school a year after their age-assigned grade level.

CONCLUSIONS

Contrary to previous study results, we observed almost no relative age effect on medication use for ADHD among children in Denmark. We postulate that this may be due to the high proportion of relatively young children held back by 1 year in the Danish school system and/or a generally low prevalence of ADHD medication use in the country.

Common Danish standards in prescribing medication for children and adolescents with ADHD

Assessing whether symptoms of attention-deficit hyperactivity disorder (ADHD) in children are age-inappropriate is essential. Hence, comparing children within one school grade is problematic and the risk of applying relative standards is inherent. Being young-for-grade increases the likelihood of receiving medication in countries with high prevalence of ADHD medication. We test the same hypothesis in a cohort of 418,396 children and find no difference between children who are young-for-grade and old-for-grade. The Danish system, with its restrictive approach to medication and clear diagnostic guidelines seems to have avoided a systematic bias of ADHD medication in young children reported in other countries.

Relative immaturity and ADHD: findings from nationwide registers, parent- and self-reports

BACKGROUND

We addressed if immaturity relative to peers reflected in birth month increases the likelihood of ADHD diagnosis and treatment.

METHODS

We linked nationwide Patient and Prescribed Drug Registers and used prospective cohort and nested case-control designs to study 6-69 year-old individuals in Sweden from July 2005 to December 2009 (Cohort 1). Cohort 1 included 56,263 individuals diagnosed with ADHD or ever used prescribed ADHD-specific medication. Complementary population-representative cohorts provided DSM-IV ADHD symptom ratings; parent-reported for 10,760 9-year-old twins born 1995-2000 from the CATSS study (Cohort 2) and self-reported for 6,970 adult twins age 20-47 years born 1959-1970 from the STAGE study (Cohort 3). We calculated odds ratios (OR:s) for ADHD across age for individuals born in November/December compared to January/February (Cohort 1). ADHD symptoms in Cohorts 2 and 3 were studied as a function of calendar birth month.

RESULTS

ADHD diagnoses and medication treatment were both significantly more common in individuals born in November/December versus January/February; peaking at ages 6 (OR: 1.8; 95% CI: 1.5-2.2) and 7 years (OR: 1.6; 95% CI: 1.3-1.8) in the Patient and Prescribed Drug Registers, respectively. We found no corresponding differences in parent- or self-reported ADHD symptoms by calendar birth month.

CONCLUSION

Relative immaturity compared to class mates might contribute to ADHD diagnosis and pharmacotherapy despite absence of parallel findings in reported ADHD symptom loads by relative immaturity. Increased clinical awareness of this phenomenon may be warranted to decrease risk for imprecise diagnostics and treatment. We speculate that flexibility regarding age at school start according to individual maturity could reduce developmentally inappropriate demands on children and improve the precision of ADHD diagnostic practice and pharmacological treatment.