Conceptual Perspectives on Selecting the Principal Variables in the Purchasing Managers' Index
研究了如何选择采购经理指数（PMI）的关键变量，发现基于就业扩散指数的简化PMI与现有加权方法相比信息损失不大，且表现更优。
The current research investigates the choice of principal variables for computing the Purchasing Managers' Index (PMI). To this end, the principal components variable selection strategy considered by Jolliffee (1972, 1973) is applied to monthly data on five key diffusion indexes for the period from January 1948 to October 2004, compiled by the Institute for Supply Management (ISM). Results do not support the ISM's current practice of assigning different weights to the five diffusion indexes (i.e., the highest weight to the new orders diffusion index and the lowest one to the inventory diffusion index). Findings also support that a simpler PMI based solely on the employment diffusion index, one of the five key PMI indicators, can be computed without loss of too much information. In many cases, the PMI series offered in this paper outperforms the PMI series proposed by others.