I analyze the comovement of US prices and output in the postwar period.
I use a new set of statistics to characterize the comovement between variables. The
statistics capture important information about the dynamics in the system. The estimation
procedure does not require assumptions about the order of integration or the types
of assumptions needed for VAR decompositions. I "nd that the comovement between
output and prices is positive in the &short run' and negative in the &long run'. I show that
a model in which demand shocks dominate in the short run and supply shocks dominate
in the long run can explain these empirical results, while sticky-price models with only
demand shocks cannot.