Development and validation of an index score to adjust for healthy user bias in observational studies

摘要

Objectives To develop a healthy user index to serve as a method of confounding adjustment in future observational studies of preventive therapies. Methods A large administrative database of patients with type 2 diabetes was split in half randomly, yielding deriva- tion and validation cohorts. Influenza vaccination was used as a 'prototypical marker' of a healthy user. In our derivation cohort, we fitted a mixed effects logistic regression model, and a points-based system was used to construct the index. The healthy user index was then evaluated in the validation cohort. Results Overall, 13% had received the influenza vaccination. In the derivation cohort (n = 914 732), the healthy user index ranged from 0 to 91 with a mean of 41.6 (SD 12.9). When applied to the validation cohort (n = 913 231), the index ranged from 0 to 96 (mean 41.6, SD 12.9) and significantly predicted influenza vac- cination with a c-statistic of 0.649 (95% CI = 0.647-0.650). Conclusion Our healthy user index combined age, sex, and healthy behaviours to predict healthy users within admin- istrative datasets. This index score may allow for better adjustment of healthy user bias in health services research; however, external validation is further required.