Simulation studies of age-specific lifetime major depression prevalence

Area of Science:

• Epidemiology
• Mental Health Research
• Biostatistics

Background:

• Lifetime prevalence (LTP) of Major Depressive Disorder (MDD) is the proportion of a population meeting criteria for MDD during their life.
• Observed LTP typically increases in youth, stabilizes in adulthood, and declines in middle age, contrary to expectations of a steady increase.
• Explanations for this pattern include cohort effects, recall failure, differential mortality, and declining age-specific incidence.

Purpose of the Study:

• To explore patterns of incidence, recall, and mortality in relation to observed LTP patterns using a simulation model.
• To validate and calibrate the simulation model using data from the Canadian Community Health Survey (CCHS 1.2).

Main Methods:

• A simulation model was developed to investigate the interplay of incidence, recall bias, and mortality.
• The model was calibrated and validated using lifetime prevalence estimates from the 2002 Canadian Community Health Survey, Mental Health and Wellbeing (CCHS 1.2).

Main Results:

• Simulations indicate that incidence rates declining with age, coupled with recall failure, realistically predict observed LTP patterns.
• Differential mortality may influence prevalence in older age groups but is not the primary driver of the overall pattern.
• Cohort effects could explain the pattern only under assumptions of a substantial (10-fold) increase in risk for recent birth cohorts.

Conclusions:

• The age-specific pattern of MDD lifetime prevalence is most plausibly explained by incidence decreasing with age and incomplete recall of past depressive episodes.
• A cohort effect is not required to interpret the observed age-specific lifetime prevalence of Major Depressive Disorder.