Marginal analysis of a population-based genetic association study of quantitative traits with incomplete longitudinal data

A common study to investigate gene-environment interac- tion is designed to be longitudinal and population-based. Data arising from longitudinal association studies often contain missing responses. Naive analysis without taking missingness into account may produce invalid inference, especially when the missing data mechanism depends on the response process. To address this issue in the analysis concern- ing gene-environment interaction effects, in this paper, we adopt an in- verse probability weighted generalized estimating equations (IPWGEE) approach to conduct statistical inference. This approach is attractive because it does not require full model specification yet it can provide consistent estimates under the missing at random (MAR) mechanism. We utilize this method to analyze data arising from a cardiovascular disease study.