Introduction
Methods
Inclusion criteria
Exclusion criteria
Analysis
Results
Study | Country | Data source | Sample size | Years studied | Ages studied | School starting age | Symptoms/diagnosis/medication | Symptom measures | Diagnosis definition | Medications definition | NOS and comments |
---|---|---|---|---|---|---|---|---|---|---|---|
Studies from countries with high prescribing rates | |||||||||||
Elder (2010) [27] | USA | Early Childhood Longitudinal study-Kindergarten Cohort | 11784 | 1998–2007 | Not stated | 6 years of age. Date cut-off December 31st and August 31st, variable between states | Symptoms, diagnosis, medication | Parents’ reports, Teachers’ reports | Parents’ reports | Parent report-Methylphenidate, amphetamine based drugs | 5 |
Evans (2010) [15] | USA | National health interview Survey (NHIS) Medical Expenditure Panel Survey (MEPS), Nationwide private healthcare company | NHIS 35343, MEPS 31641, Private 18559 | 1997–2006; 1996–2006; 2003–2006 | 7–17 years | 6 years, cut-off date not specified | Diagnosis, medication | n/a | Self-report | Self-report and private insurance company claims Methylphenidate. Amphetamine | 5 |
Hoshen (2016) [23] | Israel | Health insurance data, covers 50% of the population | 1013149 | 2006–2011 | 6–17 years | The year in which the child turns 5, the date cut-off is variable in december based on lunar calendar | Medication | n/a | Prescriptions as a proxy for diagnosis | Prescriptions reimbursed amphetamine, methylphenidate, methamphetamine and atomoxetine | 6 removed children born in November (youngest for year) from analysis due to high rates of holding back |
Morrow (2012) [28] | Canada | Database information from Pharmanet, Medical Services Plan, Canadian Institute for Health information Discharge Abstracts Database | 937943 | 2007–2008 | 6–12 years | Calendar year in which child turns 6 years of age | Medication | n/a | n/a | Methylphenidate, dextroampheamine, mixed amphetamine salts, atomoxetine | 5 |
Schmiedeler (2015) [35] | Germany | Survey of 34 schools in in the area of Baden-Württemberg | 928 | Not stated | 1st–4th school grades | Year during which child turns 6 years of age. Cut-off not stated | Not stated | Teacher reports | Reported by teachers | Reported by teachers | 3 |
Schwandt (2016) [20] | Germany | Administrative medical claims records from all physicians registered with the social health insurance | 7.2 million | 2008–2011 | 4–14 years | Year during which child turns 6 years of age, date cut-off variable between states | Diagnosis, Medication | n/a | Database registered diagnosis | Methylphenidate or atomoxetine | 6 Relative age effect present even with different date cut-offs. Extra data provided by authors |
Zoega (2012) [16] | Iceland | Database of drug prescriptions | 11785 | 2003–2009 | Children born in 1994, 1995 and 1996 | Calendar year in which child turns 6 years of age | Medication | n/a | Prescription used as a proxy for diagnosis | Amphetamine, methylphenidate, atomoxetine | 6 |
Studies from other countries | |||||||||||
Chen (2016) [29] | Taiwan | Taiwan National Health Insurance Research Database | 378881 | 1997–2011 | 4–17 years | September 1st-August 31st academic year in which child turns 6 years of age | Diagnosis, Medication | n/a | ICD 9 code 314, given at least twice by board certified psychiatrists during follow up | Methylphenidate or atomoxetine | 6 Relative age effect not seen in years 1998–1999, 2000–2001, 2002–2003, 2008–2009. Only seen in <12 year olds |
Dalsgaard (2012) [17] | Denmark | Danish Psychiatry Central Register | 416744 | 1990–2001 | 7 + years | Calendar year in which a child turns 7 years of age | Diagnosis | n/a | Registered diagnosis | n/a | 6 |
Dalsgaard (2014) [8] | Denmark | Danish civil registration system | 418396 | 1990–2001 | 7 + years | Calendar year in which a child turns 7 years of age | Medication | n/a | n/a | Dexamphetamine, methylphenidate or atomoxetine | 6 Extra data provided by authors |
Halldner (2014) [25] | Sweden | Swedish total population migrations and cause of death registers. National patient register. Prescribed drug register | 56263 ADHD individuals, 10 random controls per case | 2005–2009 | 6–69 years | Calendar year in which child turns 7 years of age | Symptoms, diagnosis, medication | Parent reported symptoms, selfreported symptoms | Coded in register or prescription as a proxy | Prescription in register Amphetamine, dexamphetamine, methylphenidate, atomoxetine | 6 Extra data provided by authors |
Karlstad (2017) [30] | Norway | Norwegian prescription database, Norwegian Patient Registry | 509827 | 1998–2006 | 6–14 years | Calendar year in which child turns 6 years of age | Diagnosis, medication | n/a | Database diagnosis of ADHD either from specialist or GP | Methylphenidate, atomoxetine, racemic amphetamine, dexamphetamine, lisdexamphetamine | 6 |
Krabbe (2014) [31] | The Netherlands | GP surgeries | 2218 | Not stated | 5–12 years | October 1st-September 31st academic year in which child turns 5 years of age | Medication | n/a | Methylphenidate as a proxy for diagnosis | GP prescriptions. Methylphenidate only | 4 Authors omitted all children born October and November from analysis to try and exclude those held back a year |
Librero (2015) [32] | Spain | Health department Sistema de Informacion Poblacional | 20237 | Not stated | 6–12 years | Calendar year in which child turns 6 years of age | Medication | n/a | Medication prescription used as a proxy for diagnosis | Methylphenidate, atomoxetine | 5 |
Pottegard (2014) [18] | Denmark | The Danish National Prescription Registry, Danish Student Register, Danish Civil Registration System | 932032 | 2000–2012 | 7–12 years | Calendar year in which child turns 7 years of age | Medication | n/a | n/a | Methylphenidate, atomoxetine, modafinil | 6 |
Rivas-Juesas (2015) [33] | Spain | Retrospective case control study of patients referred to a neurology clinic | 3469 | 1992–2012 | Up to 15 years | Calendar year in which child turns 6 years of age | Diagnosis | n/a | Diagnosis based on assessment made in clinic | n/a | 4 |
Folgar (2017) [34] | Spain | Sampled from Schools in Galacia | 1547 | Not stated | 6th grade of primary school and 1st grade of secondary school | Calendar year when child turns 6 years of age | Diagnosis | n/a | Self-report | n/a | 3 |
Studies not included in the meta-analyses | |||||||||||
Gokce (2016) [26] | Turkey | First and second grades of all public primary schools in Kadikoy county | 3696 | Not Stated | First and second school grades | 60–66 months, cut-off date not specified | Diagnosis | n/a | Self-report | n/a | 3 Not included. Comparison made dependent on age starting school, not relative age within school year |
Sayal (2017) [19] | Finland | National Registers | 6136 | 1998–2011 | 7–17 years | Calendar year in which child turns 7 years of age | Diagnosis | n/a | Individual registered within the Finnish Hospital Discharge Register with a diagnosis of ADHD | n/a | 6 Not included. Data presented do not include the total number of participants per group |
Whiteley (2017) [24] | Australia | Pharmaceutical Benefits Scheme | 311384 | 2013 | 6–10, 11–15 years | The academic year from 1st July–30th June when the child turns 5 years | Medication | n/a | n/a | Not listed | 5 Not included. No data published on group totals |