Research on CDHPs must address the observational nature of the data; neither this paper, nor
any other in the last two to three decades, has run an experiment and randomly assigned health
insurance plans with variable cost sharing. The options for identifying the effect of CDHPs as
they are currently offered are limited. One option some have pursued is to compare those
enrolling in CDHPs to those working for the same firms but enrolling in other plans with lower
cost sharing. This avoids firm level selection but is subject to individual level selection bias. An
alternative used by a few study teams is to focus only on full-replacement firms, those that
choose to offer only CDHP(s) to all their employees