12.15. For the 2014 GSS, when we regress y = number of hours per day watching TV on s = sex (1 = male, 0 = female)

and religious affiliation (r1 =1 for Protestant, r2 = 1 for Catholic, r3 = 1 for Jewish, r1 = r2 = r3 = 0 for none or other), we get ˆy = 2.7 + 0.1s + 0.4r1 + 0.2r2 − 0.2r3.

(a) Interpret the coefficient of r1.

(b) State a corresponding model for the population, and indicate which parameters must equal zero for y to be independent of religious affiliation, for each sex.