Direct effects and effect among the treated

Researchers are frequently interested in assessing the direct effect of one variable on an outcome of interest, where this effect is not mediated through a set of intermediate variables. In this chapter, we will examine direct effects in a gender salary equity study example. Such studies provide one measure of the equity of procedures used to set salaries and of decisions in promoting and advancing faculty based on performance measures. The goal is to assess whether gender, as determined at birth, has a direct effect on the salary at which a faculty member is hired, not mediated through intermediate performance of the subject up until the time the subject gets hired. If such a direct effect exists, then that means the salary was set in response not only to merit but also to the gender of the person, indicating a gender inequality issue.