Using Email And Letters To Reduce Choice Errors Among ACA Marketplace Enrollees.

During the 2019 open enrollment period in California's Affordable Care Act (ACA) Marketplace, we used a randomized intervention to examine the effects of email and postal messages on choice errors, where low-income households enroll in gold or platinum plans although they are eligible for cost-sharing reduction (CSR) silver plans with lower premiums and higher actuarial values. Relative to the control group, assignment to the email-only treatment increased plan switching to CSR silver plans by 2 percentage points (an 11 percent increase), and assignment to the mail-plus-email treatment increased plan switching to CSR silver plans by 3.9 percentage points (a 22 percent increase). The mail-plus-email treatment significantly increased plan switching across all subpopulations in which choice errors were made. Consumers who switched out of a plan chosen in error saved an average of $84 per month in premiums and $56 per month in reduced out-of-pocket expenses. Our results indicate that low-cost nudges can help low-income enrollees obtain more generous coverage at a lower price and that the combination of email and postal messages is more effective at increasing plan switching than email alone to rectify choice errors.