What strategies would you employ to handle time-varying confounders in a longitudinal study?
Instruction: Describe methods for adjusting for time-varying confounders and provide an example where such methods are necessary.
Context: This question evaluates the candidate’s ability to manage complex confounding structures that change over time in a longitudinal data setup.
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A time-varying confounder changes during follow-up and helps determine both subsequent treatment and the outcome. It need not be affected by earlier treatment. When it is affected by earlier treatment, ordinary regression that adjusts for every updated value can block part of the treatment effect or introduce bias. I would start with the treatment strategies, outcome horizon, and order of measurements...