Applying the illness-death model to estimate the incidence and remission of severe anxiety and depressive symptoms in the German National Cohort (NAKO).
BACKGROUND: Epidemiological evidence on the incidence and remission of anxiety and depressive disorders is limited. We estimated age- and sex-specific incidence and remission rates of moderate-to-severe anxiety and depressive symptoms using the illness-death model. METHODS: The German National Cohort (NAKO) is a cohort of over 200,000 participants aged 19-74 at baseline. Prevalence of probable cases, estimated with the Generalized Anxiety Disorder Scale and the Patient Health Questionnaire data 2014-2019 across five regions, was related to general mortality rates and disorder-specific mortality rate ratios in the illness-death model. The partial derivative of prevalence was modeled as a function of incidence and remission, with parameters estimated via least-squares optimization through 2,000 bootstrap resamples. RESULTS: The highest incidence rates (per 1,000 person-years) occurred at ages 19-21 for anxiety symptoms: 4.07 (95% CI: 0.00-7.57) in women and 2.55 (0.00-4.94) in men; and at ages 28-34 for depressive symptoms: 4.41 (0.00-9.81) in women and 3.30 (0.00-7.34) in men, all in Hamburg. Remission rates (per 100 person-years) were highest at older ages. For anxiety symptoms, rates peaked at 71.8 years in women (4.10 [0.00-11.94]) and 64.2 years in men (3.00 [0.00-9.23]) in Freiburg. For depressive symptoms, the highest observed was at 74.0 years, both among women (6.61 [0.00-15.50] in Münster) and men (3.58 [0.00-11.51] in Berlin). CONCLUSIONS: Incidence and remission rates of anxiety and depressive symptoms can be estimated from prevalence and mortality data, revealing regional, sex-, and age-related variation. Validation with longitudinal data is warranted.