Researchers Analyzed Records of Hospitalization for Heart Disease in Two

Multiple Choice

Researchers analyzed records of hospitalization for heart disease in two Ohio cities,Bowling Green and Kent.A city ordinance enacted in Bowling Green banned smoking in public areas.Results indicated that hospitalization rates for the two cities were similar before the smoking ban,but hospitalization rates decreased in Bowling Green compared to Kent following the smoking ban.A potential threat to internal validity that will need to be ruled out is

A) the amount of information about heart disease presented in national media.
B) changes in the state sales tax on cigarettes.
C) changes in doctors' focus on symptoms of heart disease in Bowling Green (because of publicity for the ban) , but not in Kent.
D) all of these