Introductory Econometrics 4th Edition by Jeffrey Wooldridge

Exercise 16

The data set BWGHT.RAW contains data on births to women in the United States. Two variables of interest are the dependent variable, infant birth weight in ounces (bwght), and an explanatory variable, average number of cigarettes the mother smoked per day during pregnancy (cigs). The following simple regression was estimated using data on n = 1,388 births:
(i) What is the predicted birth weight when cigs = 0 What about when cigs = 20 (one pack per day) Comment on the difference.
(ii) Does
this simple regression necessarily capture a causal relationship between the child's birth weight and the mother's smoking habits Explain.
(iii) To predict a birth weight of 125 ounces, what would cigs have to be Comment.
(iv) The proportion of women in the sample who do not smoke while pregnant is about.85. Does this help reconcile your finding from part (iii)