Individual-level Wage Data Before-and-After Program Completion

In explaining the importance of individual-level “before-and-after ” wage data, we note that economists generally refer to such data as longitudinal data or panel data. Economists use these terms, rather than “before-and-after data, ” although the meanings of these three labels are practically the same. In the following discussion, we will refer to authors who refer to longitudinal data or to panel data in their research. Professor Cheng Hsiao of the University of Southern California wrote a working paper entitled “Why Panel Data? ” [1]. This technical document explains the many reasons why modern economists and researchers have come to rely upon longitudinal data. “There is a proliferation of panel data studies…In 1986, there were 29 studies listing the key words: “panel data or longitudinal data, ” according to Social Sciences Citation index. By 2003, there were 580, and in 2004, there wer