Interindustry and Interregion Differentials: Mechanics and Interpretation
指出Krueger和Summers关于行业工资差异的经典方法存在标准误计算问题，提出只需简单矩阵运算即可得到精确估计，近似方法会高估标准误并低估差异的总体变异性。
In their seminal study on interindustry wage differentials, Krueger and Summers (1988) expressed estimated industry differences as deviations from a hypothetical employment-share weighted mean. Virtually the whole labor literature has followed their approach, yet most studies avoid calculating the exact standard errors of these differences. This note relates this problem to the general literature on dummy variables and their interpretation. It is demonstrated that the implementation of exact estimates involves only simple matrix operations, making any approximative procedure difficult to justify. Disregarding this conclusion will in practice, even with large samples, lead to substantially overstated standard errors of the estimated differentials and to the understatement of their overall variability. © 1997 by the President and Fellows of Harvard College and the Massachusetts Institute of Technology