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