Consumer demand theory states that the quantity demanded of a commodity DX is a function of, or depends on, its price PX , consumer's income Y , and the price of other (related) commodities, say, commodity Z (i.e., PZ ). Assuming that consumers' tastes remain constant during the period of analysis, state the preceding theory in

(a) speci?c or explicit linear form or equation and

(b) in stochastic form.

(c) Which are the coe?cients to be estimated? What are they called?