Abstract
We study the relationship between hours worked and technology during the postwar period in the US. We show that the responses of hours to technological improvements have increased over time, and that the patterns captured by the SVAR are consistent with those obtained from an RBC model with a less than unitary elasticity of substitution between capital and labor. Data supports the hypothesis that the observed changes in the response of hours to a technology shock are attributable to changes in the magnitude of the degree of capital-labor substitution. We argue that the observed time-variation in can arise from changes in the structural composition of sectors (or factors) in a heterogeneous inputs production function or from biases in technological change.