Recent interest in trade union activity has led to the development of econometric models of union membership growth. This paper examines the structural stability of two of the leading models—Ashenfelter-Pencavel's and Bain-Elsheikh's—each of which claimed to have captured the primary determinants of union growth in the twentieth century. The models were reestimated using revised, corrected, and extended membership data, and a nonlinear, maximum-likelihood procedure was employed to estimate the shift-point for each model. Contrary to previous studies, we found evidence of a break in the structure of each model. And unlike earlier work that hypothesized a World War II break-point, our estimated point was 1937–1938, most likely reflecting the impact of the Wagner Act.

A framework is developed for decomposing product price changes into changes in input prices, technical efficiency, and deviations of price from unit cost. This framework facilitates the measurement of productivity growth in noncompetitive industries. The history of American steel rail prices between 1879 and 1910 is analyzed, and it is concluded (in contrast with much recent work) that productivity growth remained rapid until the twentieth century and that the steel industry was sufficiently collusive so that the rail producers received the benefits of that productivity growth as excess profits.

D O the poor substitute among commodities more flexibly than the rich when relative prices change, even when compensated for the income effects of the price changes? Is it necessary to add a third dimension to the Slutsky substitution matrix to identify household income? In short, do the terms of the Slutsky elasticity matrix curve smoothly from poor households to rich households in such a way that equation (1) is meaningful?