This paper examines the power of statistical tests commonly used to evaluate the efficiency of speculative markets. It shows that these tests have very low power. Market valuations can differ substantially and persistently from the rational expectation of the present value of cash flows without leaving statistically discernible traces in the pattern of ex-post returns. This observation implies that speculation is unlikely to ensure rational valuations, since similar problems of identification plague both financial economists and would be speculators.

ABSTRACT This paper examines the power of statistical tests commonly used to evaluate the efficiency of speculative markets. It shows that these tests have very low power. Market valuations can differ substantially and persistently from the rational expectation of the present value of cash flows without leaving statistically discernible traces in the pattern of ex‐post returns. This observation implies that speculation is unlikely to ensure rational valuations, since similar problems of identification plague both financial economists and would be speculators.

This paper develops a model of dual labor markets based on employers' need to motivate workers. In order to elicit effort from their workers, employers may find it optimal to pay more than the going wage. This changes fundamentally the character of labor markets. The model is applied to a wide range of labor market phenomena. It provides a coherent framework for understanding the claims of industrial policy advocates. It also can provide the basis for a theory of occupational segregation and discrimination that will not be eroded by market forces. Finally, the model provides the basis for a theory of involuntary unemployment.

This paper investigates transitory components in stock prices. After showing that statistical tests have little power to detect persistent deviations between market prices and fundamental values, we consider whether prices are mean-reverting, using data from the United States and 17 other countries. Our point estimates imply positive autocorrelation in returns over short horizons and negative autocorrelation over longer horizons, although random-walk price behavior cannot be rejected at conventional statistical levels. Substantial movements in required returns are needed to account for these correlation patterns. Persistent, but transitory, disparities between prices and fundamental values could also explain our findings.