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.

Immune response in paper wasp workers: Task matters more than age

Workers of social hymenopterans (ants, bees and wasps) display specific tasks depending on whether they are younger or older. The relative importance of behavior and age in modulating immune function has seldom been addressed. We compared the strength of encapsulation-melanization immune response (hereafter melanotic encapsulation) in paper wasps displaying age polyethism or experimentally prevented from behavioral specialization. Foragers of Polybia paulista had higher melanotic encapsulation than guards, regardless of their age. Nevertheless, melanotic encapsulation decreased with age when wasps were prevented from behavioral specialization. Thus, in this species, worker melanotic encapsulation seems more sensitive to task than age. Foraging is considered one of the riskier behaviors in terms of pathogen exposure, so upregulating melanotic encapsulation in foragers can possibly improve both individual and colony-level resistance against infections.

Relative age in the school year and risk of mental health problems in childhood, adolescence and young adulthood

PURPOSE

Relative age within the school year ('relative age') is associated with increased rates of symptoms and diagnoses of mental health disorders, including ADHD. We aimed to investigate how relative age influences mental health and behaviour before, during and after school (age range: 4-25 years).

METHOD

We used a regression discontinuity design to examine the effect of relative age on risk of mental health problems using data from a large UK population-based cohort (Avon Longitudinal Study of Parents and Children (ALSPAC); N = 14,643). We compared risk of mental health problems between ages 4 and 25 years using the parent-rated Strengths and Difficulties Questionnaire (SDQ), and depression using self-rated and parent-rated Short Mood and Feelings Questionnaire (SMFQ) by relative age.

RESULTS

The youngest children in the school year have greater parent-rated risk of mental health problems, measured using parent-rated SDQ total difficulties scores. We found no evidence of differences before school entry [estimated standardised mean difference (SMD) between those born on 31 August and 1 September: .02 (-.05, .08)]. We found that estimates of effect size for a 1-year difference in relative age were greatest at 11 years [SMD: .22 (.15, .29)], but attenuated to the null at 25 years [SMD: -.02 (-.11, .07)]. We did not find consistent evidence of differences in self-rated and parent-rated depression by relative age.

CONCLUSIONS

Younger relative age is associated with poorer parent-rated general mental health, but not symptoms of depression.

Relative age effect in elite Brazilian athletes in different combat sports: an observational study

Background

The relative age effect (RAE) suggests that, due to maturity, young athletes born in the first quartiles of the year may have advantages over those born in the last quartiles of the year. Thus, it is important to evaluate the RAE in different sports and to consider the particularities of the subdivisions of the sports categories.

Objective

To analyze the RAE in the top 20 of the Brazilian rankings in different combat sports.

Methods

Observational study that analyzed the national databases for the year 2019 (from categories U-11 to U-18) made publicly available by the Brazilian confederations of karate, taekwondo and fencing. We obtained data on date of birth, age category and body weight of all modalities, type of fencing competition weapon (Epee, Foie and Saber) and type of karate modality (kumite and kata) from the top 20 places in each ranking. The final sample consisted of 1,486 athletes (Age: 14.2 ± 2.3. Male-53.2%. Female-46.8%). To identify the RAE, we performed a contingency analysis and compared the results between the sexes within the same sport.

Results

There was RAE in the U-11, U-12, U-15 and U-17 fencing categories (p < 0.05), being higher in the female categories (p < 0.05). The RAE was higher for males in the Epee test, and similar between the sexes for the Saber and Foie tests. In karate, RAE occurred in categories U-14 and U-16 (p < 0.05), being higher in males (p < 0.05). The RAE was similar between the sexes in the kumite modality (p < 0.05). There was no RAE for the kata modality in karate (p > 0.05) and for the Taekwondo categories (p > 0.05).

Conclusion

The results showed the existence of a relative age effect in elite athletes ranked (top 20 places in each ranking) only for the sport of fencing and karate kumite.

Graphical abstract

Effect of relative age on diagnosis of autism spectrum disorder in children: a nationwide study in Taiwan

BACKGROUND

The annual cut-off birthdate for entry into school in Taiwan is August 31. Thus, children and adolescents born in August are typically the youngest in their grades. The potential effect of relative age on the diagnosis of autism spectrum disorder (ASD) remains uncertain.

METHODS

A total of 9,548,393 individuals aged 3-17 years during the study period (from September 1, 2001, to August 31, 2011) identified from the Taiwan National Health Insurance Research Database were enrolled into our study. Logistic regression analysis was used to examine the likelihood of receiving ASD diagnosis 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 likelihood of being diagnosed with ASD (odds ratio [OR]: 1.24, 95% confidence interval [CI]: 1.16-1.32; OR: 1.23, 95% CI 1.06-1.42) than did those born in September. Sensitivity analysis conducted over different periods revealed consistent findings.

DISCUSSION

Relative age, as an indicator of neurocognitive maturity, is a crucial contributor to the risk of being diagnosed with ASD among children and adolescents. Our findings highlight the importance of considering the age of a child within a grade when diagnosing ASD.

Age within schoolyear and attention-deficit hyperactivity disorder in Scotland and Wales

BACKGROUND

Previous studies suggest an association between age within schoolyear and attention-deficit hyperactivity disorder (ADHD). Scotland and Wales have different school entry cut-off dates (six months apart) and policies on holding back children. We aim to investigate the association between relative age and treated attention deficit hyperactivity disorder (ADHD) in two countries, accounting for held-back children.

METHODS

Routine education and health records of 1,063,256 primary and secondary schoolchildren in Scotland (2009-2013) and Wales (2009-2016) were linked. Logistic regression was used to examine the relationships between age within schoolyear and treated ADHD, adjusting for child, maternity and obstetric confounders.

RESULTS

Amongst children in their expected school year, 8,721 (0.87%) had treated ADHD (Scotland 0.84%; Wales 0.96%). In Wales, ADHD increased with decreasing age (youngest quartile, adjusted OR 1.32, 95% CI 1.19-1.46) but, in Scotland, it did not differ between the youngest and oldest quartiles. Including held-back children in analysis of their expected year, the overall prevalence of treated ADHD was 0.93%, and increased across age quartiles in both countries. More children were held back in Scotland (57,979; 7.66%) than Wales (2,401; 0.78%). Held-back children were more likely to have treated ADHD (Scotland OR 2.18, 95% CI 2.01-2.36; Wales OR 1.70, 95% CI 1.21-2.31) and 81.18% of held-back children would have been in the youngest quartile of their expected year.

CONCLUSIONS

Children younger within schoolyear are more likely to be treated for ADHD, suggesting immaturity may influence diagnosis. However, these children are more likely to be held back in countries that permit flexibility, attenuating the relative age effect.

Do You Really Want to Be Forever Young? Emotional Health and Psychosocial Well-being by Relative Birth Quarter in Canadian Adolescents

PURPOSE

Those born earlier within cohorts of similarly aged children tend to outperform peers in athletic and academic pursuits. Subsequent evidence suggests relatively younger children may also experience worse emotional and psychosocial health; however, evidence from middle adolescents is limited. This study assessed whether depression, anxiety, and psychosocial well-being differed by the relative birth quarter (RBQ) within a cohort of grades 9-12 in secondary schools across Canada.

METHODS

Data from the 2018-19 student self-report surveys of the cannabis use, obesity, mental health, physical activity, alcohol use, smoking, and sedentary behavior study were analyzed. Students having made normative progress were categorized into RBQs by the provincial enrollment cutoff date (n = 49,921). Hierarchical modeling approaches assessed whether self-reported depression, anxiety, psychosocial well-being, and positive controls differed by RBQ after controlling for covariates.

RESULTS

Despite relative age effects for positive control outcomes, no significant difference was detected for anxiety and depression scores or likelihood of meeting thresholds for having clinically relevant symptoms. However, a significant difference emerged between RBQs for psychosocial well-being scores; post hoc tests found that psychosocial well-being scores were lower in the fourth RBQ than those in all prior quarters.

DISCUSSION

Results agree with limited findings that relative age differences in emotional health are not significant in older cohorts. Nonetheless, relatively older individuals reported very small (d = .04-.05) advantages in psychosocial well-being than their youngest peers, which aligns with previous data. Longitudinal approaches to assess relative age effects on mental health during and throughout the transition into middle adolescence are warranted.

Competition age: does it matter for swimmers?

OBJECTIVE

To establish reference data on required competition age regarding performance levels for both sexes, all swimming strokes, and race distances and to determine the effect of competition age on swimming performance in the context of other common age metrics. In total, 36,687,573 race times of 588,938 swimmers (age 14.2 ± 6.3 years) were analyzed. FINA (Fédération Internationale de Natation) points were calculated to compare race times between swimming strokes and race distances. The sum of all years of race participation determined competition age.

RESULTS

Across all events, swimmers reach top-elite level, i.e. > 900 FINA points, after approximately 8 years of competition participation. Multiple-linear regression analysis explained up to 40% of variance in the performance level and competition age showed a stable effect on all race distances for both sexes (β = 0.19 to 0.33). Increased race distance from 50 to 1500 m, decreased effects of chronological age (β = 0.48 to - 0.13) and increased relative age effects (β = 0.02 to 0.11). Reference data from the present study should be used to establish guidelines and set realistic goals for years of competition participation required to reach certain performance levels. Future studies need to analyze effects of transitions between various swimming strokes and race distances on peak performance.

Hill on a mountaintop: A longitudinal and cross-sectional analysis of the relative age effect in competitive youth football

The aim of this study was to examine the origin and persistence of the relative age effect (RAE) in competitive youth football. To examine its origin, birthdates of 121 category one Premier League academy players recruited over 6 years were compared with 691 Under 8 (U8) players in one of the regional grassroots leagues from which academy players are selected. To examine the persistence of the RAE we conducted a longitudinal comparison of retention rates in early-birth and late-birth academy players from U9 to U15, and made a cross-sectional comparison of birthdate distributions from U7 to U18 in 10,857 regional league players. The results revealed birthdate asymmetry in both the academy and grassroots players but a much larger RAE in the academy. Longitudinal analysis revealed that the cumulative probability of retention at the academy was higher for early-birth than late-birth players. A small to medium RAE persisted across grassroots football age groups though it declined somewhat from U15 to U18. The implication of these results for academy player recruitment is discussed.

Moderating factors influence the relative age effect in Australian cricket

BACKGROUND

The relative age effect is a commonly occurring phenomenon whereby there is a tendency for relatively older players to be over-represented during high level competitions. This effect is often seen to diminish as player's age, however, there has been far less investigation on other potential moderating factors.

METHOD

This study investigated the impact of the relative age effect, and potential moderating factors, within the talent selection process of Australian cricket. Relative age distribution of 2,415 male and female junior and senior state level cricket players, who played in the Junior National Championships or State competition (senior level) between 2011 and 2015, were analysed.

RESULTS

Players born in the first quartile of the cricket season were significantly over-represented in both male Under-15, Under-17, Under-19 and female Under-15 and Under-18 levels. However, there was no significant difference at the senior state level for either male or female cricketers. Further investigation of the relative age effect in the junior talent pathway revealed that male all-rounders, batters and pace bowlers, and female all-rounders and batters, born in first quartile were over-represented. Right-handed batters and bowlers were also influenced by the relative age effect at all Junior National levels, while left-handed batters and bowlers were only influenced at the Under-15 and Under-17 levels. These results highlight the impact relative age has on junior cricket talent pathways, including sex, age, handedness and primary skills. Only state level, and left-handedness at the Under-19 level, were unaffected by relative age.

DISCUSSION

The findings of this study highlight the influence of relative age effects for both male and female junior cricket players. Interestingly, there may be an advantage to being left-handed that is more prevalent at the older (male Under-19; female Under-18) age levels.

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.

Younger children experience lower levels of language competence and academic progress in the first year of school: evidence from a population study

BACKGROUND

The youngest children in an academic year are reported to be educationally disadvantaged and overrepresented in referrals to clinical services. In this study we investigate for the first time whether these disadvantages are indicative of a mismatch between language competence at school entry and the academic demands of the classroom.

METHODS

We recruited a population sample of 7,267 children aged 4 years 9 months to 5 years 10 months attending state-maintained reception classrooms in Surrey, England. Teacher ratings on the Children's Communication Checklist-Short (CCC-S), a measure of language competence, the Strengths and Difficulties Questionnaire-Total Difficulties Score (SDQ), a measure of behavioural problems, and the Early Years Foundation Stage Profile (EYFSP), a measure of academic attainment, were obtained at the end of the reception year.

RESULTS

The youngest children were rated by teachers as having more language deficits, behaviour problems, and poorer academic progress at the end of the school year. Language deficits were highly associated with behaviour problems; adjusted odds ratio 8.70, 95% CI [7.25-10.45]. Only 4.8% of children with teacher-rated language deficits and 1.3% of those with co-occurring language and behaviour difficulties obtained a 'Good Level of Development' on the EYFSP. While age predicted unique variance in academic attainment (1%), language competence was the largest associate of academic achievement (19%).

CONCLUSION

The youngest children starting school have relatively immature language and behaviour skills and many are not yet ready to meet the academic and social demands of the classroom. At a population level, developing oral language skills and/or ensuring academic targets reflect developmental capacity could substantially reduce the numbers of children requiring specialist clinical services in later years.

The Extent and Specificity of Relative Age Effects on Mental Health and Functioning in Early Adolescence

PURPOSE

Although extensive evidence indicates that being younger within a school cohort is associated with poorer academic functioning, much less is known about such relative age effects (RAEs) for mental health--the focus of the current investigation.

METHODS

Data from 23,379 11- to 13-year-olds attending state-maintained secondary schools in England were analyzed to investigate RAEs on mental health measured using the Strengths and Difficulties Questionnaire. Participants were grouped into oldest, middle, and youngest thirds of their academic year based on their month of birth relative to their cohort. Hierarchical linear regression analysis evaluated RAEs and gender- or deprivation-related moderation of such effects.

RESULTS

Relatively younger adolescents had significantly more emotional symptoms and peer problems compared with relatively older individuals in a year group, although effect sizes were small. These effects were not moderated by gender or deprivation. Impact of mental health difficulties on other aspects of functioning was also greater among relatively younger children. Larger RAEs are observed in the younger cohort (11-12 years) compared with those in the 12- to 13-year-olds, thereby indicating that RAEs might attenuate with age.

CONCLUSIONS

Being relatively younger than classmates is associated with increased internalizing symptoms, poorer peer relationships, and higher impact of mental health difficulties on functioning at school and home. The findings support wider inclusion of relative age in understanding mental health difficulties and its inclusion as a potential risk factor in studies investigating the development of psychopathology, especially for internalizing symptoms. Possible mechanisms of the effects detected are discussed.

Young for one's grade: a risk factor for psychotic experiences among adults in the National Comorbidity Survey-Replication

School-related difficulties have received relatively little attention as environmental risk factors for psychotic experiences (PEs), despite being characterized by marginalization and social defeat during critical periods of psychological development. This study examined both childhood age relative to one's classmates and school mobility as risk factors for adult psychotic experiences in the National Comorbidity Survey-Replication (NCS-R). Weighted logistic regression models were used to explore the hypotheses that lifetime psychotic experiences reported on the World Health Organization psychosis screen would be more prevalent among those younger than their classmates during childhood and for those with frequent school mobility. Younger perceived relative age (odds ratio (OR)=2.05, 95% confidence interval=1.43-2.95) was independently associated with psychotic experiences in the fully adjusted model, but school mobility was not. School-related risk factors for psychosis provide promising points for community-level intervention, and support the claim that environmental factors characterized by disadvantage and marginalization contribute to psychosis etiology.