U.S. firms' stock return volatility rose fivefold from 1971 through 2000 and then reverted to near 1971 levels by 2006. This was driven mainly by a rise and fall in the firm-specific, rather than systematic, component of volatility. Firm-level total factor productivity growth volatility exhibited a similar pattern. We hypothesize that firm heterogeneity, reflected in firm-specific volatility, rises as a new general purpose technology (GPT) propagates across the economy and then ebbs once the GPT is widespread. Measuring GPT adoption by information technology capital intensity, we find robust cross-industry empirical evidence supporting the hypothesis.

In this paper, we examine the sources of the productivity growth in the U.S. computer industry from 1978 to 1999. We estimate a joint production model of output quantity and quality that distinguishes two types of technological changes: process and product innovations. Based on the estimation results, we decompose total factor productivity (TFP) growth rate into the contributions of process and product innovations and scale economies. We find that product innovation associated with better quality accounts for about 30% of the TFP growth in the computer industry. Furthermore, the TFP acceleration in the computer industry in the late 1990s is mainly derived from a rapid increase in product innovation.

This paper examines the effect of information technology (IT) on the relative demand for educated workers in U.S. industries from 1960 to 1996. After decomposing this effect into IT use and adoption, I find that the use of IT is complementary with educated workers, and that educated workers have a comparative advantage in the adoption of IT. In total, IT use and adoption effects account for almost 40% of the acceleration in demand for educated workers since 1970. Moreover, the adoption of IT explains about one-third of the total IT effect on the acceleration in skill upgrading in the 1970s.