Why are workers with identical skills found in both "good" jobs and "bad" jobs? Why are workers who do similar jobs paid differently, contrary to standard competitive theory? Observable differences in workers doing the same job account for only 30 percent of wage variation. In Wage Dispersion, Dale Mortensen examines the reasons for pay differentials in the other 70 percent. He finds that these differentials, or wage dispersion, are largely the result of job search friction (which arises when workers do not know the wages offered by all employers) and cross-firm differences in wage...