Triggered by the recent financial crisis, the regulation of banks has gained new traction among academics, regulators, and politicians. One of the key challenges in effective regulation is time inconsistency of regulation. While a regulator would like to commit not to bail out banks in order to set the right ex-ante incentives, this threat is generally not credible since the government does not follow through in the event of a crisis. Banks therefore have an incentive to expose themselves to risk that is partially insured by the government.
To mitigate this problem, regulators attempt to reduce the likelihood of banking crises by regulating both banks’ asset side and liability side. While there has been a recent push to focus on the liability side by mandating higher equity capital requirements, the very nature of a deposit-taking institution implies that leverage is an integral part of the business model of banks, unlike for other firms. In this paper, we therefore focus on the regulation of banks’ asset holdings. The starting point of our paper is the natural assumption that a regulator cannot directly observe the riskiness of assets, but needs to rely on an external (private) assessment of risk. Since the introduction of the Basel I framework, credit ratings have played an important role in bank regulation as “objective” measures of credit risk. This role has been confirmed in the Basel III (2011) guidelines, which still rely on credit ratings as measures of creditworthiness.