Statistical Analyses
We calculated the incidence and prevalence of screening positive for postpartum depression based on the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition -IV Childhood Diagnoses and Edinburgh Postnatal Depression Scale and its subscales (Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition-7, Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition-3, and Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition-2) at 6weeks, 3 months, and 6 months postpartum. In our sensitivity and specificity estimates, we considered a Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition -IV Childhood Diagnoses diagnosis to be the criterion standard (ie, gold standard) for the diagnosis of a major depressive disorder. Because each participant completed the screening instruments at 3 postpartum visits, we used a repeated-measures longitudinal modeling approach using generalized estimating equations with an exchangeable correlation structure because of the intraparticipant correlation over repeated visits. Predicted probabilities were derived from the generalized estimating equation model and were then used to construct receiver operating characteristic ( receiver operating characteristic ) curves and to compute the areas under the curve (area under the curves).