Adjusting for risk selection in state health insurance exchanges will be critically important and feasible, but not easy.

The Affordable Care Act calls for the establishment of state-level health insurance exchanges. The viability and success of these exchanges will require effective risk-adjustment strategies to compensate for differences in enrollees' health status across health plans. This article describes why the Affordable Care Act could lead to favorable or adverse risk selection across plans. It reviews provisions in the act and recent proposed regulations intended to mitigate the problem of risk selection. We performed a simulation that showed that under the premium rating restrictions in the law, large incentives for insurers to attract healthier enrollees will be likely to persist-resulting in substantial overpayment to plans with very healthy enrollees and underpayment to plans with very sick members. We conclude that risk adjustment based on patients' diagnoses, such as will be in place from 2014 on, will yield payments to insurers that will be more accurate than what will come solely from the age-adjusted and other rating allowed by the act. We also describe additional challenges of implementing risk adjustment.