Portfolio Substitution and the Effects of Bank Capital Regulation
Abstract
Banks allocate their portfolios across different types of loans and securities. A large literature finds that stronger capital requirements reduce bank lending, but these studies generally estimate the total bank-level response to a change in regulation that shifts multiple assets’ regulatory penalties simultaneously in a predetermined pattern. Evaluating counterfactual policies that impose a different pattern of regulatory penalties across assets from those observed in the data requires modeling how an asset’s supply responds to its own regulatory cost as well as to the costs of other assets. I develop a structural framework and empirical method to estimate asset-level own-cost supply elasticities separately from portfolio substitution. For identification, I use changes in bank-level capital requirements that alter assets’ regulatory penalties by different amounts, while the model’s portfolio adding-up constraint links each asset’s supply to the regulatory costs of all other assets. My method recovers positive supply elasticities for every asset category, with securities holdings responding more to regulatory costs than loans do. Applying these elasticities to post-crisis capital requirements, I ask whether stronger capital regulation explains large banks’ shift from lending to securities since the financial crisis. I argue that capital regulation accounts for about 28% of this shift since 2011.
