HEDIS measures and managed care enrollment.

This article examines the relationship between 1996 health plan enrollment and both HEDIS-based plan performance ratings and individual HEDIS measures. Data were obtained from a large firm that collected, aggregated, and disseminated plan performance ratings to its employees. Plan market share regressions are estimated controlling for out-of-pocket price and model type in addition to the plan ratings and HEDIS measures. The results suggests that employees did not respond strongly to the provided ratings. There are several potential explanations for the lack of response, including difficulty understanding the ratings and never having seen them. In addition, employees may base their plan choices on information that is obtained from their own past experience, friends, family, and colleagues. The pattern of results suggests that such information is important. Counterintuitive signs most likely reflect an inverse correlation between some HEDIS ratings (or measures) and attributes employees observe informally.