Regulatory Treatment of Changes in Fair Value and the Composition of Banks' Investment Portfolios

In their implementation of Basel III, U.S. bank regulators are again including changes in the fair value of available-for-sale (AFS) debt securities in Tier 1 capital, but only for the largest U.S. banks. This paper investigates a potential impact of expanding this regulation by examining bank investment decisions in the 1990's when changes in the fair value of AFS debt securities were included in regulatory capital for all banks. Using a matched sample difference-in-differences research design, we find evidence that low-capitalized banks reduced their investments in more volatile asset classes (e.g., corporate bonds, non-agency MBS) and increased their investments in less volatile asset classes (e.g., treasuries and municipal bonds) after changes in fair value were included in regulatory capital. We also find that low-capitalized banks change their holdings of these asset classes in the opposite direction after regulators subsequently excluded changes in fair value from regulatory capital. These findings inform regulators worldwide regarding a possible consequence of Basel III. We also contribute to prior research by suggesting that changes in maturity and credit risk around the passage of SFAS 115 (Beatty 1995; Hodder, Kohlbeck, and McAnally 2002) were partially obtained by changing the composition of asset classes within banks' investment portfolios.