Portfolio Substitution and the Effects of Bank Capital Regulation
Abstract
A large literature finds that bank capital requirements reduce lending, but these studies generally estimate lending responses to regulations that change required equity for multiple bank assets simultaneously. For example, a 1-percentage-point increase in a bank’s risk-based capital requirement raises the required equity on risk-weight-1 loans by 1 percentage point and on risk-weight-0.2 securities by 0.2 percentage points. Evaluating counterfactual policies that impose a new pattern of equity requirements across assets, such as changing a single asset’s risk weight, requires estimating the response of an asset’s supply to its own regulatory cost while holding other assets’ costs fixed. I develop a portfolio-allocation model and empirical method to estimate asset-level supply elasticities using changes in bank-level capital requirements. The model uses the fact that portfolio shares sum to one to separate each asset’s response to its own regulatory cost from portfolio substitution. I recover positive supply elasticities for every asset category, with securities holdings responding more to regulatory costs than loans do. Applying these elasticities to post-crisis requirements, I ask whether capital regulation explains large banks’ shift from lending to securities. Capital regulation accounts for about 28% of the aggregate shift toward securities and 35% of the cross-sectional convergence in large banks’ average asset risk weights since 2011.
