In the literature, comparisons between absolute levels of productivity in different
industries occur frequently. This paper explores the meaning and possible significance
of such measures. Prices must be used to permit the required comparison of the outputs
of different industries. It is shown that base-year weights produce a valid measure
of productivity growth but not of absolute productivity level. Current price weights
do yield a valid index of absolute productivity but one that tends to be equal for
all industries because of the general equilibrium mechanism that reallocates resources
from low-productivity to high-productivity industries.