# Applying the illness-death model to estimate the incidence and remission of severe anxiety and depressive symptoms in the German National Cohort (NAKO)

## TL;DR

This study estimates how often severe anxiety and depression start and improve in Germany, using a model that combines health and death data.

## Contribution

The study introduces a novel application of the illness-death model to estimate incidence and remission rates of anxiety and depression.

## Key findings

- Anxiety incidence peaks in young women (age 19–21) and depression in middle-aged women (age 28–34).
- Remission rates increase with age, with the highest rates observed in older adults.
- Regional differences in incidence and remission rates were identified across German cities.

## Abstract

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.

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.

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).

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.