1. In a method of determining preferences of persons viewing broadcast television programs on television display sets located in rooms of private homes, the improvement comprising in combination: humanly imperceptibly sensing proximity of persons to television sets within viewing distance in rooms for which permission to effect said sensing has been obtained, by sensing invisible infrared radiation emanating from human bodies and other sources of infrared radiation in said rooms; automatically correlating said imperceptibly sensed proximity individually to television programs broadcast for display by television display sets in said rooms and elsewhere; and electronically determining from said correlated sensing what broadcast television programs were viewed in which rooms.