Equilibrium Theory Might Be Appropriate for a Planned or a Primitive Economy, But Is Not Appropriate for a Modern Market Economy

Equilibrium theory might well be appropriate for a planned economy, or perhaps for a very primitive subsistence economy, where little changes, and one year is much like the next. But it is quite unhelpful in understanding how a modern market economy works. Some of the most important elements of the contemporary economy, such as institutions, entrepreneurship and profits, are missing, while some extreme assumptions which contradict experience, such as perfect knowledge, optimising behaviour and constant returns to scale, have been introduced into the theory in order to achieve predictability. The justification of equilibrium theory therefore rests not on its explanatory power but on its predictive ability. On this point the evidence is overwhelming. All surveys of forecasting accuracy come to the same conclusion: economic forecasts based on equilibrium theory perform no better than naive forecasts which assume that next year’s values will be the same as this year’s.

—David Simpson, introduction to Rethinking Economic Behaviour: How the Economy Really Works (Houndmills, UK: Macmillan Press, 2000), 3.