"Correlation and Regression"

Biddle and Hamermesh (1990) built a multiple regression model to study the tradeoff between time spent in sleeping and working and to look at other factors affecting sleep:

Sleep = β0 + β1 totwrk + β2 educ + β3 age + ε

where sleep and totwrk (total work) are measured in minutes per week and educ and age are measured in years. Suppose the following equation is estimated:

Sleep = 3500 – 0.15 totwrk – 11.20 educ + 2.29 age + ε

Discuss what would happen to someone’s sleep if they choose to work more.
Analyze whether the factors of totwrk, educ, and age are enough factors to explain the variation in sleep. Explain which additional factors should be explored in order to explain the variation in sleep. Provide your reasoning.