<qa>  What is the major advantage of our approach?We will take advantage of an ongoing natural experiment whereby employers have shifted all their employees at once from traditional insurance to HDHPs. We will use the strongest quasi-experimental, longitudinal methods available to compare the experience of patients switched by their employers into HDHPs with contemporaneous patients whose employers remain in traditional plans. A major advantage of our approach is the inclusion of only employers whose employees had no choice of insurance plans, minimizing member-level selection bias. 