Part of the downfall came early and on theoretical grounds, with the realization that real-world information lags for aggregate variables like the pr… - Robert J. Gordon

The original Lucas version of the new-classical macroeconomics combined the undeniable appeal of rational expectations with two more dubious assumptions inherited from Friedman (1968), that is, continuous market clearing and imperfect information, to form the foundation of the famous “Lucas supply function” (more justly, the Friedman-Lucas supply function). Soon Sargent and Wallace (1975) extracted from Lucas’s model its implication for monetary policy, the famous “policy-ineffectiveness proposition.” The demonstration by Barro (1977) 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.

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 (RBC) model, which was also based on continuous market clearing and competitive equilibrium, but now generated the business cycle through serially correlated procyclical technology shocks.

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 (1981). 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."