This paper develops a new technique for measuring the effect of computer usage on U.S. productivity growth. Standard National Income and Product Accounts (NIPA) measures of the computer capital stock, which are constructed by weighting past investments according to a schedule for economic depreciation (the rate at which capital loses value as it ages), are shown to be inappropriate for growth accounting because they do not capture the effect of a unit of computer capital on productivity. This is due to technological obsolescence: machines that are still productive are retired because they are no longer near the technological frontier, and anticipation of retirement affects economic depreciation. Using a model that incorporates obsolescence, alternative stocks are developed that imply a larger computer-usage effect. This effect, together with the direct effect of increased productivity in the computer-producing sector, accounted for the improvement in U.S. productivity growth over 1996-1998 relative to the previous twenty years.

The canonical inflation specification in sticky-price rational expectations models (the new-Keynesian Phillips curve) is often criticized for failing to account for the dependence of inflation on its own lags. In response, many studies employ a “hybrid” specification in which inflation depends on its lagged and expected future values, together with a driving variable such as the output gap. We consider some simple tests of the hybrid model that are derived from its closed form. We find that the hybrid model describes inflation dynamics poorly, and find little empirical evidence for the type of rational, forward-looking behavior that the model implies.

This paper analyzes the stability over time of the econometric process for euro-area inflation since 1970, focusing in particular on the behavior of the so-called persistence parameter (the sum of the coefficients on the lagged dependent variables). Perhaps surprisingly, in light of the Lucas critique, our principal finding is that there appears to be relatively little instability in the parameters of the euro-area inflation process. Full-sample estimates of the persistence parameter are generally close to 1, and we fail to reject the hypothesis that this parameter has been stable over time. We discuss how these results provide some indirect evidence against rational expectations models with strong forward-looking elements, such as the New Keynesian Phillips curve.