Economists analyzing a well-conducted randomized controlled trial or natural experiment and finding a statistically significant effect conclude that the null of no effect is unlikely to be true. But how frequently is this conclusion warranted? The answer depends on the proportion of tested nulls that are true and the test's power. I model the distribution of t-statistics in leading economics journals. Using my preferred model, 65% of narrowly rejected null hypotheses and 41% of all rejected null hypotheses with |t|<10 are likely to be false rejections. For the null to have only a .05 probability of being true requires a t of 5.48.

Prior to trade liberalization in the 1980s, New Zealand heavily protected low‐wage industries. Consequently, trade liberalization was desirable from the perspective of both traditional and new trade theories. While liberalization decreased employment in protected industries somewhat, it also significantly affected wages, noticeably diminishing the effect of liberalization on employment in previously protected industries and thus reducing the postliberalization shift in the industrial composition of employment. The small effect of liberalization on the composition of employment suggests that the effect of tariffs on wages and firms' monopoly power substantially eliminated any effect of protection on the distribution of employment.

In his valuable contribution, After Civil Rights, John Skrentny shows that in many sectors of the labor market, race is used in ways that were unanticipated when the 1964 Civil Rights Act was enacted. With separate chapters on the professions and business, the public sector, media and entertainment, and the low-skill market, he demonstrates that the new racial realism is widespread, generally has some justification from social scientific research, and is usually inconsistent with judicial decisions. I review the racially realistic practices (racial matching, increasing diversity, racial signaling, and racial characteristics) and discuss their implications for labor economics and for policy.

Any advanced industrial society is composed of a number of speech communities with different verbal and nonverbal languages. In particular, in the United States blacks and whites and men and women have sharply differing methods of speaking and listening. This paper develops a model in which people can only work together if they "speak" the same language and in which it is costly to learn a second language. The competitive market will tend to minimize communication through segregation, but if interaction is required, the cost will be borne by the minority. A number of nontrivial predictions are derived from the model.

We develop an estimator that allows us to calculate an upper bound to the fraction of unrejected null hypotheses tested in economics journal articles that are in fact true. Our point estimate is that none of the unrejected nulls in our sample is true. We reject the hypothesis that more than one-third are true. We consider three explanations for this finding: that all null hypotheses are mere approximations, that data-mining biases reported standard errors downward, and that journals tend to publish papers that fail to reject their null hypotheses only when the null hypotheses are likely to be false. While all these explanations are important, the last seems best able to explain our findings.

Under the educational sorting hypothesis a state compulsory school attendance law will increase the educational attainment of high-ability workers who are not directly affected by the law. Under the human capital hypothesis such laws affect only those individuals whose behavior is directly constrained. We find that compulsory attendance laws do increase enrollment rates in age groups they do not affect directly. Thus, our results contradict the human capital hypothesis and are consistent with the sorting hypothesis.

We review theories of race discrimination in the labor market. Taste-based models can generate wage and unemployment duration differentials when combined with either random or directed search even when strong prejudice is not widespread, but no existing model explains the unemployment rate differential. Models of statistical discrimination based on differential observability of productivity across races can explain the pattern and magnitudes of wage differentials but do not address employment and unemployment. At their current state of development, models of statistical discrimination based on rational stereotypes have little empirical content. It is plausible that models combining elements of the search models with statistical discrimination could fit the data. We suggest possible avenues to be pursued and comment briefly on the implication of existing theory for public policy.