At 12 weeks gestation, mothers’ questionnaires included an item asking whether they had ever had severe depression. Responses endorsing current or past depression were scored as 1; a response of “no, never” was scored 0. This binary variable was included as a covariate in secondary analyses in order to control for the potential effects of rater bias (Fergusson et al., 1993; Najman et al., 2001).
