How can governments limit excessive and unstable credit growth? Should they raise capital requirements for banks? In our recent NBER working paper, Does Macropru Leak? Evidence from a UK Policy Experiment, we address these questions using evidence from a policy experiment in the UK. The minimum capital ratio requirements that national regulatory authorities impose on banks have two sets of objectives: (i) so-called ‘micro-prudential’ motives, to ensure the safety and soundness of individual banks; and (ii) ‘macro-prudential’ goals, especially to influence the aggregate supply of credit. Micro-prudential regulation has a long pedigree, but the focus on macro-prudential regulation has increased sharply in the wake of the global financial crisis. This sharpened focus underlies recent changes in the international regulatory regime for banks. Basel III, as the new regime is called, establishes a “countercyclical capital buffer”, under which national regulators would vary banks’ required capital-to-risk-weighted assets ratio over time, thereby helping smooth the credit cycle. For variation in minimum capital requirements to be effective in regulating the aggregate supply of credit, three conditions must be satisfied:

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