We have the following estimation result with Y= expenditure on food ($), X= after-tax income ($) and D=1 for female and D=0 for male: [25% for each sub-question]

i = 1506.244 - 228.987 Di + 0.059 Xi

s.e. = (188.009) (107.058) (0.006) t = (8.012) (-2.138) (9.641)

s.e.=standard error. t - critical value at the 5% level: 2.179.

a) What is the research question based on the model specification? What is the role of D?

b) Interpret the coefficients on D and X?

c) Derive the confidence interval for the slope coefficient at the 5% significance level. Comment on the result. d) Based on the estimation result, write two models: one for female and the other for male.