Question

1. Consider the following estimated outcome: bwght = 119.77-0.514cigs Where bwght-infant birth weight in ounces; cigs-average number of cigarettes the mother smoked per day during pregnancy. (1) What is the predicted birth weight when cigs=0? What about when cigs-20(one pack per day)? Comment on the difference. (2) Does this simple regression necessarily capture a causal relationship between the child's birth weight and the mother's smoking habits? Explain. (3) To predict a birth weight of 125 ounces, what would cigs have to be? Comment (4) The proportion of women in the sample who do not smoke while pregnant is about 0.85.Does this help reconcile your finding from part(3).

Answer 1

When cigs = 0, then birth weight will be 119.77 ounces When cigs = 20, then birth weight will be 119.77 -0.514(20) = 109.49 ounces This means as number of cigarettes smoked by the mother increases by 20 unit, then birthweight will fall by 10.28 ounces b) Not necessarily, as there might be many other factors affecting child birth weight, and no just the number of cigarettes smoked bwght = 119.77-0.514 cigs 125 = 119.77 -0.514 cigs Cigs = -10.17 cigarettes This is not possible since cigs cannot be negative Hence, achieving a birth weight of 125 ounces is not possible under the given regression equation Yes, the proportion of women who do not smoke if is included in the model can lead to an increase in the intercept term and thus give us new results.