In Exercise E.5 we find that males have a higher average yearly income than females, in Exercise E.6 we find that males work more hours per week than females, on average, and in Exercise E.9 we find that people who work more hours per week make a higher yearly income. Using the EmployedACS dataset:
(a) Explain why HoursWk is a confounding variable in the relationship between Income and Sex.
(b) Use multiple regression to see if Sex is a significant predictor of Income, even after accounting for the number of hours worked per week.
(c) What is the predicted yearly income for a male who works 40 hours per week? For a female who works 40 hours per week? What is the difference?

The American Community Survey, administered by the US Census Bureau, is given every year to a random sample of about 3.5 million households (about 3% of all US households). It has been crucial for government and policy decisions, and helps to determine how over 400 billion dollars of government funds are distributed each year. Unfortunately, the House voted in May 2012 to eliminate this valuable source of information. Data on a random sample of 1% of all US residents are made public (after ensuring anonymity), and we have selected a random sub-sample of n = 1000 from the 2010 data, stored in ACS.