Table 10.7 lists the mean salary, in thousands of dollars, of faculty on nine-month contracts in U.S. institutions of higher education in 2013–2014, by gender and academic rank.

(a) Suppose that gender is the explanatory variable. Identify the response variable and the control variable.

(b) Describe the bivariate relationship between gender and salary.

(c) Describe the relationship between gender and salary, controlling for academic rank.

(d) A hypothesis of interest for these variables is “Controlling for academic rank, annual salary and gender are independent.” Draw a causal diagram that is consistent with this hypothesis. Refer to your interpretation in part (c), and comment on whether the hypothesis seems plausible.

(e) Is it possible that the overall difference between mean income of men and women could be larger than the difference for each academic rank? (It nearly is.) Explain how or how not.

TABLE 10.7 Academic Rank Gender Professor Associate Assistant Instructor Overall Men 115.5 81.2 68.5 59.6 85.5 Women 98.1 75.4 63.6 56.9 70.4 Source: National Center for Education Statistics, Digest of Education Statistics, 2015, Table 316.10.