(PS7-77) Exploring Ergodic Relationship Between Depression and Worry Using Ecological Momentary Assessment (EMA)

Ergodicity refers to whether data from a group is representative of all individual members. Fisher et al. (2018) suggest that non-ergodicity in human subjects research can be a hindrance to the ability to generalize results from the group level to the individual level.  However, ergodicity can be viewed on a spectrum (Adolf and Fried, 2019). The aim of this study was to determine whether there is an ergodic relationship between depression and worry using ecological momentary assessment (EMA) data. We used an app that notified users to complete a 24 item questionnaire 5 times a day for two weeks. 

We implemented the statistical analysis outlined in Fisher et al. (2018). Specifically, ergodicity was assessed by comparing intraindividual and interindividual variations for depression and worry (N = 476). Individuals and sequential observation groups with fewer than 20 observations were excluded from the analyses. To determine the interindividual variation in correlations, the sequential observations were grouped together based on observation number (e.g. first response for all individuals were grouped together). The correlations for depression and worry were determined for each sequential observation number. To calculate intraindividual variation using raw data, the correlation between depression and worry was determined for each individual participant. We assessed ergodicity by comparing the variation in the correlations between worry and depression at the individual level and group level. 

Average intraindividual correlation  (r = 0.311, SD = 0.247)) and average interindividual correlation (r =  0.553, SD = 0.061) were both positive. Depression and worry were positively related at both the individual and group level.  Individual variability was approximately 4 times larger than group variability for depression and worry. This shows that there is greater variation at the individual level for the relationship between depression and worry than at the group level.

The findings support the conclusions presented in Fisher et al. (2018). There is greater fluctuation of depression and worry at the individual level, due to the discrepancy between the individual and group level variation. Given the difference in intraindividual variation and interindividual variation, the relationship between depression and worry is non-ergodic. Therefore, group level findings may not apply to the varying individual level experiences.