This paper develops a model of sectoral labor mobility and tests its main implications. The model nests two distinct hypotheses on the origin of mobility: (a) sectoral shocks and (b) worker-employer mismatch. We estimate the relative importance of each hypothesis and find that the bulk of labor mobility is caused by mismatch rather than by sectoral shift. We then try to put a value on society's match-specific information. That is, we ask to what extent the availability of the option to change jobs raises GNP. We find that the mobility option raises expected earnings by roughly between 8.5 percent and 13 percent of labor earnings, which translates to an increase in GNP of between 6 percent and 9 percent.

This paper compares monopsonistic and competitive search equilibria. While the competitive equilibrium is efficient, the monopsonistic equilibrium is not: there is too much search, and the employment rate is too low.

This paper develops a stochastic framework for determining transactions and precautionary demand for money. Through application of the principles of inventory management, the analysis integrates and extends the work of Baumol, Tobin, and Miller and Orr. Optimal money holdings are shown to depend on the rate of interest, on the mean and the variance of net disbursements and on the cost of portfolio adjustment. The properties of the distribution of the payment period are analyzed. The optimal solution is obtained by minimizing net present value of cost. This solution is compared with the one obtained by the conventional method of minimizing the steady-state cost.

We model merger waves as reallocation waves, and argue that mergers spread new technology in a way that is similar to that of the entry and exit of firms. We focus on two periods: 1890–1930, during which electricity and the internal combustion engine spread through the U.S. economy, and 1970–2000—the Information Age. As the model implies, reallocation did rise during both epochs. The model also implies that exits should lead mergers during a transition, but this seems to have happened more emphatically in the electrification epoch.

The Q-theory of investment says that a firm's investment rate should rise with its Q. We argue here that this theory also explains why some firms buy other firms. We find that 1. A firm's merger and acquisition (M&A) investment responds to its Q more -- by a factor of 2.6 -- than its direct investment does, probably because M&A investment is a high fixed cost and a low marginal adjustment cost activity, 2. The typical firm wastes some cash on M&As, but not on internal investment, i.e., the 'Free-Cash Flow' story works, but explains a small fraction of mergers only, and 3. The merger waves of 1900 and the 1920's, `80s, and `90s were a response to profitable reallocation opportunities, but the `60s wave was probably caused by something else.

Firms that entered the stock market in the 1990s were younger than any earlier cohort since World War I. Surprisingly, however, firms that IPO'd at the close of the 19th century were just as young as the companies that are entering today. We argue here that the electrification-era and the IT-era firms came in young because the technologies that they brought in were too productive to be kept out very long. The model assumes that the stage before IPO is a learning period during which the firm refines the idea before committing to it at the IPO stage. The better the idea, the higher is the opportunity cost of a delay in its implementation, and the earlier the firm will have its IPO.

Investment of US firms responds asymmetrically to Tobin’s Q: investment of established firms—“intensive” investment—reacts negatively to Q whereas investment of new firms—“extensive” investment—responds positively and elastically to Q. This asymmetry, we argue, reflects a difference between established and new firms in the cost of adopting new technologies. A fall in the compatibility of new capital with old capital raises measured Q and reduces the incentive of established firms to invest. New firms do not face such compatibility costs and step up their investment in response to the rise in Q.

This paper studies the evolution of a competitive industry in which a fixed number of firms reduce costs by innovating and by imitating their rivals' technologies. As the firms' technologies gradually improve, industry output expands and price falls. Technological leaders tend to rely on innovations to reduce their costs, whereas the laggards rely more on imitation. Imitation causes technology to spread from the leaders to the followers and forces some convergence of technology among firms as the industry matures. This convergence is accompanied by faster growth of smaller firms and a consequent tightening of the distribution of output over firms. Since imitation is a kind of spillover of technology, equilibrium is likely to involve insufficient innovative and imitative effort relative to a social optimum.

Firm numbers first rise, then later fall, as an industry evolves. This nonmonotonicity is explained using a competitive model in which innovation opportunities fuel entry and relative failure to innovate prompts exit; equilibrium time paths for price and quantity also share features of the data. The model is estimated using data from the U.S. automobile tire industry, a particularly dramatic example of the nonmonotonicity in firm numbers.

This paper studies the evolution of a competitive industry in which a fixed number of firms reduce costs by innovating and by imitating their rivals' technologies. As the firms' technologies gradually improve, industry output expands and price falls. Technological leaders tend to rely on innovations to reduce their costs, whereas the laggards rely more on imitation. Imitation causes technology to spread from the leaders to the followers and forces some convergence of technology among firms as the industry matures. This convergence is accompanied by faster growth of smaller firms and a consequent tightening of the distribution of output over firms. Since imitation is a kind of spillover of technology, equilibrium is likely to involve insufficient innovative and imitative effort relative to a social optimum.