Although the survey is not a panel, it distinguishes between individuals enrolled in the free care (no copay) version of the 30 Baht program (i.e., the “roll-over” portion of the MWS) from those who must pay the 30 Baht copay (i.e., those who were previously enrolled in the MWS program). This allows us to classify individuals into the three groups (UNINS, MWS, CONTROL) in each year of the survey..