"Since the late 1960s macroeconomic debates in the United States have centered on the competing interpretations of the new classical and new Keynesian macroeconomics. The initial new classical model developed in the early 1970s by Robert E. Lucas, Jr., combined market-clearing, imperfect information, and rational expectations. After much testing, it was eventually rejected in the late 1970s for failing to explain why business cycles lasted on average four years while information delays lasted only a few weeks. It was soon replaced by a second new classical approach, the Real Business Cycle model, which was also based on continuous market clearing and competitive equilibrium, but now generated the business cycle through serially correlated procyclical technology shocks."

“Part of the downfall came early and on theoretical grounds, with the realization that real-world information lags for aggregate variables like the price level and money supply were much too short to rationalize the persistent multiyear deviations from equilibrium that seemed to characterize business cycles in most industrialized countries. The second dubious assumption, continuous market clearing, was viewed more critically once it was recognized that it was not an inextricable concomitant of rational expectations, especially when Stanley Fischer and Edmund Phelps and John Taylor showed that rational expectations could be embedded in a model containing real-world institutional features like multiperiod wage and price contracts to generate nonmarket-clearing behavior. Once Fischer and Phelps-Taylor had shown that rational expectations by itself was a necessary but not a sufficient condition to validate new-classical policy conclusions, the race was on to develop the new-Keynesian theory based on rational expectations and one or another institutional impediment to continuous market clearing.”

“But business cycles as a subject for study have enjoyed a revival for at least a decade now, stimulated in part by the severity of the 1974-75 and 1981-82 recessions and in part by the intellectual ferment surrounding the development of the "equilibrium business cycle model" and the attention paid to the seminal work of Robert E. Lucas, Jr., contained in his book Studies in Business Cycle Theory . Indeed, there is no longer any need to lament the passing of economics courses explicitly carrying the title "Business Cycles," since the topic of business cycle behavior and analysis has so infiltrated courses carrying the title "Macroeconomics" that the two subjects have become almost interchangeable. 2 In this light it is fitting that the major research program of the NBER in this area is called "Economic Fluctuations" rather than "Macroeconomics.”

“Much time was wasted and ink spilled in the late 1960s and early 1970s trying to interpret the lagged effect of prices on wages as reflecting adaptive lags in the formation of expectations. But if we have learned anything from the new Keynesian economics of Fischer, Taylor, Blanchard, and their younger followers, it is that price and wage inertia is compatible with rational expectations.”

“The original Lucas version of the new-classical macroeconomics combined the undeniable appeal of rational expectations with two more dubious assumptions inherited from Friedman , that is, continuous market clearing and imperfect information, to form the foundation of the famous “Lucas supply function” . Soon Sargent and Wallace extracted from Lucas’s model its implication for monetary policy, the famous “policy-ineffectiveness proposition.” The demonstration by Barro that one could interpret historical U.S. data to be consistent with the proposition and the theory brought new-classical economics to its shortlived period of peak influence.”

“This theme of mismeasurement interacts with the designation of the one hundred years between 1870 and 1970 as the “special century.” Measurement errors are greatest in the early years, both in the scope of the standard of living and in the extent of price index bias. Clearly the welfare benefits to consumers in the categories of life entirely omitted from GDP were greatest long ago: the transition from the scrub board to the automatic washing machine was a more important contributor to consumer welfare than the shift from manual to electronic washing machine controls or from a twelve-pound tub to an eighteen pound tub. The most important unmeasured benefit of all, the extension of life expectancy, occurred much more rapidly from 1890 to 1950 than afterward.”

“New-classical economics has been undeniably influential, but not in the way that its three prominent creators originally imagined. Its most important contribution to macroeconomics, the assumption of rational expectations, was stolen almost immediately, and applied more fruitfully, by the new Keynesians.”