Problem
The file health.xls contains data for the following variables: birth_weight = the weight of infants after birth; when low this can put an infant at risk of illness; cig = number of cigarettes the mother was smoking during pregnancy; and fam_inc = the income of the family; the higher the family income the better the access to prenatal care for the family in general. We would expect that the latter two variables should affect birth_weight.
(a) Run a regression that includes both variables and explain the signs of the coefficients.
(b) Estimate a regression that includes only fam_inc, and comment on your results.
(c) Estimate a regression that includes only cig and comment on your results.
(d) Present all three regressions summarized in a table and comment on your results, especially by comparing the changes in the estimated effects and the R2 of the three different models. What does the F statistic suggest about the joint significance of the explanatory variables in the multiple regression case?
(e) Test the hypothesis that the effect of cig is two times greater than the respective effect of fam_inc, using the Wald test.
The response should include a reference list. Double-space, using Times New Roman 12 pnt font, one-inch margins, and APA style of writing and citations.