To evaluate offspring ADHD by parental ADHD and other psychiatric disorders, both prevalence rates, prevalence differences (PD) and relative risks (RR) were calculated using predicted absolute prevalence from a Poisson regression model with adjustment for year of birth (5‐year groups; Zou, 2004 (
link)). To account for correlation between siblings, we used mother’s identification number as a cluster variable in the analyses. We also calculated the parent–offspring recurrence of ADHD: (a) confined to first offspring born 1967–2011, and (b) for a narrower follow‐up period, confined to offspring born 1981–2011 whose parents were born 1967–1997, as sensitivity analyses.
We examined intergenerational recurrence risks within an epidemiological framework. Therefore, we chose epidemiological measures of associations (Khoury, Beaty, & Cohen, 1993 ). However, as a supplementary analysis, we also calculated tetrachoric correlations (mother–offspring and father–offspring) as a quantification of the genetic and environmental (familial) contributions from mother/father to offspring.
Two‐sided tests with a significance threshold of
p < .05 were used in all analyses. Analyses were carried out with
SPSS Statistics 23 (IBM Corp. Released, 2013 ) and
STATA intercooled version 14 (StataCorp, 2015 . StataCorp LP) from October 3, 2018, to October 1, 2020.
Solberg B.S., Hegvik T., Halmøy A., Skjærven R., Engeland A., Haavik J, & Klungsøyr K. (2020). Sex differences in parent–offspring recurrence of attention‐deficit/hyperactivity disorder. Journal of Child Psychology and Psychiatry, and Allied Disciplines, 62(8), 1010-1018.