The Engel expenditure curve relates a consumer's expenditure on a commodity to his or her total income. Letting Y = the consumption expenditure on a commodity and X = the consumer income, consider the following models:
a. Yi = B1 + B2Xi + ui
b. Yi = B1 + B2(l/Xi) + ui
c. In Yi = B1 + B2 In X, + ui
d. In Yi = B1 + B2(l/Xi) + ui
e. Yi = B1 + B2 In X, + ui
f. In(Y) = Bi - B2 (1/X). This model is known as the log-inverse model. Which of these models would you choose for the Engel curve and why?