Because inputs are scarce, marginal cost should be an increasing function of output. Without changes in this real marginal cost schedule, aggregate output can vary if and only if the markup of price over marginal cost varies. In this review, we discuss the extent to which observed fluctuations...

If changes in aggregate demand were an important source of macroeconomic fluctuations, real wages would be countercyclical unless markups of price over marginal cost were themselves countercyclical. We thus examine three theories of markup variation at cyclical frequencies. The first assumes...