Lucas critique

The argument that policy changes can alter people’s expectations and decisions, making historical statistical relationships unreliable for evaluating new policies.

Rational expectations: A theory that people use available information to form expectations consistent with the model of the economy. Policy announcements matter because expectations about future rules shape decisions today.
Robert E. Lucas Jr.: An American economist whose work on expectations and macroeconomic policy transformed modern macroeconomics. His 1976 paper gave the critique its clearest statement and name.
New Keynesian economics: A macroeconomic framework combining rational expectations with imperfect competition and nominal rigidities. It builds policy analysis around forward-looking behavior while retaining reasons monetary policy can affect output.
Tinbergen rule: A principle that effective policy requires at least as many independent instruments as policy targets. It addresses policy design constraints, not the stability of estimated behavioral relationships.
Policy invariance: The property that an economic relationship remains stable when policy changes. The critique rejects policy invariance for relationships shaped by expectations and choices.
Econometric Policy Evaluation: The use of statistical economic models to assess the effects of policy choices. The critique directly challenges evaluations that extrapolate historical relationships to new policies.
Dynamic stochastic general equilibrium: A macroeconomic modeling framework that represents decisions over time under uncertainty and economy-wide constraints. These models aim to evaluate policy through explicit decision mechanisms rather than fixed historical correlations.
Goodhart's law: The principle that a statistical measure can lose value as a target when people respond to its use. Both ideas warn that intervention can change the behavior behind a useful statistical relationship.
Structural model: An economic model that represents underlying relationships among preferences, technologies, constraints, and choices. Structural models aim to capture behavior that remains meaningful when policy rules change.
Keynesian economics: An economic tradition emphasizing aggregate demand, price rigidities, and the role of stabilization policy. Lucas challenged policy models that treated estimated behavioral relationships as stable across interventions.

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