The following model is a simplified version of the multiple regression model used by
Biddle and Hamermesh (1990) to study the trade-off between time spent sleeping
and working and to look at other factors affecting sleep:
sleep = β0 + β1totwrk + β2educ + β3age + u
where sleep and totwrk (total work) are measured in minutes per week and educ
(years of education) and age are measured in years.
(a) If adults trade off sleep for work, what is the sign of β1?
(b) What signs do you think β2 and β3 will have?
(c) Using the data in Biddle and Hamermesh (1990), the estimated equation is
sleep [ = 3, 638.25 â 0.148 totwrk â 11.13 educ + 2.20 age n = 706, R2 = 0.113
If someone works five more hours per week, by how many minutes is sleep
predicted to fall? Is this a large trade-off?
(d) Discuss the sign and magnitude of the estimated coefficient on educ.
(e) Would you say totwrk, educ and age explain much of the variation in sleep?
What other factors might affect the time spent sleeping? Are these likely to be
correlated with totwrk?