Sources of Advantageous Selection: Evidence from the Medigap Insurance Market.” Working Paper no. 12289

We provide strong evidence of advantageous selection in the Medigap insurance market, and analyze its sources. Using Medicare Current Beneciary Survey (MCBS) data, we nd that, conditional on controls for the price of Medigap, medical expenditures for senior citizens with Medigap coverage are, on average, about $4,000 less than for those without. But, if we condition on health, expenditures for seniors on Medigap are about $2,000 more. These two ndings can only be reconciled if those with less health expenditure risk are more likely to purchase Medigap, implying advantageous selection. By combining the MCBS and the Health and Retirement Study (HRS), we investigate the sources of this advantageous selection. These include income, education, longevity expectations and nancial planing horizons, as well as cognitive ability. Once we condition on all these factors, seniors with higher expected medical expenditure are indeed more likely to purchase Medigap. Surprisingly, risk preferences do not appear to be a source of advantageous selection. But cognitive ability emerges as a particularly important factor, consistent with a view that many senior citizens have diculty understanding Medicare and Medigap rules