OMITTED VARIABLES IN THE MEASUREMENT OF A LABOR QUALITY INDEX: THE CASE OF SPAIN
研究发现，西班牙劳动力质量增长被传统方法高估，因为忽略了不同社会人口群体生产率的相对变化和大量低能力工人涌入的影响，这解释了该国全要素生产率负增长的现象。
Traditional measures of labor quality might have the shortcoming of missing some features of the very important increase in labor utilization within European countries. In particular, we explore the case of Spain. Despite showing one of the most important increases in labor quality in the EU according to standard methods, it also presents a negative TFP growth. The paper shows the importance of considering—on top of observed changes in the composition of the labor force by gender, age, education, tenure, and nationality—changes in both average and relative productivities of those abovementioned socio‐demographic groups over time. We first use a time varying weight index in order to capture the decrease in relative productivities across characteristics. Once this issue is considered the estimated growth of labor quality decreases notably and the index becomes flat between 2002 and 2006. We relate this slowdown to the increasing over‐education of the Spanish workforce in the recent past. We then incorporate a selection model into the labor force. We argue that in the recent past there has been a massive entry of workers with below average unobserved abilities, generating a decrease in quality of labor. Indeed labor quality slightly decreased from 1995 onwards (always increasing without the selection model).