Rational expectations
Rational expectations is a hypothesis in economic theory asserting that individuals form predictions of future economic variables as the best possible unbiased estimates using all available information, such that systematic forecast errors are absent and expectations incorporate an understanding of the underlying economic model.[1] This concept implies that agents' expectations are equivalent to the mathematical conditional expectation given the information set, rendering prediction errors random and uncorrelated with known data.[2] Formulated initially by John F. Muth in a 1961 analysis of price movements in competitive markets, the idea posits that expectations are "rational" insofar as they efficiently utilize probabilistic models of the economy rather than relying on adaptive extrapolations from past errors.[3] In macroeconomics, rational expectations gained prominence through the work of Robert Lucas and Thomas Sargent in the 1970s, challenging traditional Keynesian models by demonstrating that systematic monetary policy could not exploit predictable errors in private forecasts, as agents would anticipate and neutralize such interventions.[4] This led to the Lucas critique, which argues that historical econometric relationships may fail under policy changes because agents adjust their behavior based on rational foresight of those shifts, invalidating predictions from reduced-form models estimated on past data.[5] Key implications include the neutrality of anticipated policy in the short run and the emphasis on modeling expectations explicitly in dynamic stochastic general equilibrium frameworks, influencing central bank practices like inflation targeting.[6] Despite its influence in reshaping macroeconomic theory and policy evaluation, rational expectations faces empirical scrutiny, with survey data on inflation forecasts often revealing persistent biases and incomplete information use that deviate from strict rationality assumptions.[7] Critics argue the hypothesis overstates agents' computational capacities and access to information, particularly in heterogeneous or uncertain environments, leading to alternative models incorporating bounded rationality or learning dynamics.[8] Nonetheless, it remains a benchmark for assessing expectation formation, underscoring the causal role of private beliefs in economic outcomes over naive adaptive schemes.[9]