Roman Frydman

"Early critics pointed out REH’s fundamental epistemological flaws. … They argued that REH, even if viewed as a bold abstraction or approximation, is grossly inadequate for representing how even minimally reasonable profit seeking participants forecast the future in real-world markets. Nevertheless, … an overwhelming majority of economists has embraced REH as the way to represent how rational individuals think about the future."

"Nowhere have REH’s epistemological flaws and empirical disappointments been more apparent than in efforts to model financial market outcomes, which are largely driven by participants’ expectations. Beginning with Robert Shiller’s (1981) pathbreaking paper, research has shown that REH models are unable to explain the basic features of fluctuations and risk in stock markets. Likewise, in their magisterial work on the current state of international macroeconomics, Maurice Obstfeld and Kenneth Rogoff (1996: 625) concluded that “the undeniable difficulties that international economists encounter in empirically explaining nominal exchangerate movements are an embarrassment, but one shared with virtually any other field that attempts to explain asset price data.” The failures of REH explanations of aggregate outcomes gave rise to alternative approaches, most notably behavioral finance models. However, sober assessments even by the likes of Obstfeld and Rogoff did not dispel the faith of most economists that REH models would one day be able to explain financial market outcomes and macroeconomic performance."