We study optimal securitization in the agency mortgage-backed securities (MBS) market. Many MBS are traded in the liquid to-be-announced (TBA) market, which however induces adverse selection due to cheapest-to-deliver pricing . We find that lenders pool high-value loans separately and trade them in a less liquid market. We estimate a model of MBS pooling and trading to study welfare implications of pooling policies. TBA market structure produces a trade-off between efficiency and equity; broader pooling increases liquidity and average welfare, but results in a larger cross-subsidy from smaller loans to larger loans. Minimizing costs or limiting strategic pooling results in a more regressive redistribution.

By allowing different agency mortgage-backed securities (MBS) to be traded based on limited characteristics, the to-be-announced (TBA) market generates liquidity and benefits the MBS market broadly. We quantify effects of the TBA structure on mortgage borrowers. Exploiting discontinuities in TBA eligibility, we estimate that TBA eligibility reduces mortgage rates by 7 to 28 basis points. The TBA eligibility benefit is larger for mortgages with higher expected prepayments. We also find that TBA eligibility affects refinancing, which has implications for monetary policy transmission. Our finding is relevant for housing policies, such as housing finance reforms and uniform MBS.

This paper studies the impact of advertising as a channel for risk selection in Medicare Advantage. We provide evidence that insurer advertising is responsive to the gains from risk selection. Then we develop and estimate an equilibrium model of Medicare Advantage with advertising, allowing rich individual heterogeneity. Our estimates show that advertising is effective in attracting healthy individuals who are newly eligible for Medicare, contributing to advantageous selection into Medicare Advantage. Moreover, risk selection through advertising substantially lowers premiums by improving insurers' risk pools. The distributional implication is that unhealthy consumers may be better off through cross-subsidization from healthy individuals.

We study how intermediaries – mortgage servicers – shaped the implementation of mortgage forbearance during the COVID-19 pandemic and use servicer-level variation to trace out the causal effects of forbearance on borrowers. Forbearance provision varied widely across servicers. Small servicers, nonbanks, and especially nonbanks with small liquidity buffers, facilitated fewer forbearances and saw a higher incidence of forbearance-related complaints. Easier access to forbearance substantially increased mortgage nonpayment but also reduced delinquencies outside of forbearance. Part of the liquidity from forbearance was used to reduce credit card debt, but most was saved or used for nondurable consumption.