We observed substantial differences and limited overlap between symptom-based and register-based PPD. Register-based measures capture hospital-based diagnoses and pharmacological treatment only, but not all treatment within the healthcare system, and differences may reflect a combination of severity, symptom transience, misclassification, and timing of measurement. Consistency in exposure-outcome associations varied, particularly for certain exposures. Our findings underline the importance of considering both the nature and implications of PPD definitions in epidemiological research.
Egsgaard et al. (Tue,) studied this question.