You can find that sort of statement in many principles textbooks. As George Reisman recently has pointed out, the statement is dead wrong if the implicit cost of sexual relations between spouses is added into GDP--as it should be, if it is also legitimate to include the implicit rent of owner-occupied housing. After all, only a relatively few men have sexual relations with their housekeepers, while a rather large percentage have sexual relations with their wives. The implicit cost of such relations is, of course, what a man would have to pay a prostitute for those same services. Because the rates of prostitutes far exceed those of housekeepers, if a man married his housekeeper GDP would go up. Sam Bostaph