Using the data in SLEEP75 (see also Problem 3 in Chapter 3), we obtain the estimated equation sleep 5 3,840.83 2 .163 totwrk 2 11.71 educ 2 8.70 age 1235.112 1.0182 15.862 111.212 1 .128 age2 1 87.75 male 1.1342 134.332 n 5 706, R2 5 .123, R2 5 .117.

The variable sleep is total minutes per week spent sleeping at night, totwrk is total weekly minutes spent working, educ and age are measured in years, and male is a gender dummy.

(i) All other factors being equal, is there evidence that men sleep more than women? How strong is the evidence?

(ii) Is there a statistically significant tradeoff between working and sleeping? What is the estimated tradeoff?

(iii) What other regression do you need to run to test the null hypothesis that, holding other factors fixed, age has no effect on sleeping?