Modeling and estimating the feedback mechanisms among depression, rumination, and stressors in adolescents

Abstract

The systemic interactions among depressive symptoms, rumination, and stress are important to understanding depression but have not yet been quantified. In this article, we present a system dynamics simulation model of depression that captures the reciprocal relationships among stressors, rumination, and depression. Building on the response styles theory, this model formalizes three interdependent mechanisms: 1) Rumination contributes to 'keeping stressors alive'; 2) Rumination has a direct impact on depressive symptoms; and 3) Both 'stressors kept alive' and current depressive symptoms contribute to rumination. The strength of these mechanisms is estimated using data from 661 adolescents (353 girls and 308 boys) from two middle schools (grades 6-8). These estimates indicate that rumination contributes to depression by keeping stressors 'alive'-and the individual activated-even after the stressor has ended. This mechanism is stronger among girls than boys, increasing their vulnerability to a rumination reinforcing loop. Different profiles of depression emerge over time depending on initial levels of depressive symptoms, rumination, and stressors as well as the occurrence rate for stressors; levels of rumination and occurrence of stressors are stronger contributors to long-term depression. Our systems model is a steppingstone towards a more comprehensive understanding of depression in which reinforcing feedback mechanisms play a significant role. Future research is needed to expand this simulation model to incorporate other drivers of depression and provide a more holistic tool for studying depression.

Fig 1. The depression-rumination conceptual model.

Boxed variables represent stocks (or states), and double arrows with valves depict flows into/out of the stocks. Single-line arrows present hypothesized causal relationships—their strength is estimated below. A stock variable, which is mathematically represented as an integral, is the accumulation of the difference between its inflows and outflows.

Fig 2. Distribution of memory time for girls and boys.

Fig 3. Sixteen categories of girl participants.

D₀, R₀, S₀, and SI represent initial depressive symptoms and rumination, prior stressors, and ongoing stressors, respectively.

Fig 4. Simulated depressive symptoms over 120 months for 16 groups of girls with characteristics listed in Fig 3.

Fig 5. Depressive symptoms at time 120 by rumination and ongoing stressors for a simulated girl whose prior stressors and depressive symptoms are set at the mean.