In Reply We appreciate having the opportunity to respond to Sonis’ concerns regarding our article on advancing paternal age (APA) at childbearing.1 The population and within-family estimates responded to different research questions. The population estimates examined how common it is that offspring born to fathers of different ages have psychopathology. On the other hand, the comparison of differentially exposed siblings and cousins using fixed-effects models examined the magnitude of the risk for psychopathology in offspring associated with paternal age while holding other factors constant.
D’Onofrio BM, Sjölander A, Lichtenstein P. Fixed-Effects Models and Diagnosing Psychiatric Disorders—Reply. JAMA Psychiatry. 2014;71(9):1078-1079. doi:10.1001/jamapsychiatry.2014.693