Relationship Between Parkinson's Disease And Smoking Habits

In order to examine if there was a link between Parkinson's Disease and smoking habits, scientists conducted a case-control study involving a cohort of 50,002 men who attended Harvard and the University of Pennsylvania. The subjects were given medical evaluations upon college entrance at the time of the study and a series of follow-up mailed questionnaires were sent out to the subjects following their graduation, resulting in a 70% response rate. Four control subjects were randomly selected for each case from the self-reporting subjects in one of these questionnaires, and all of these control subjects satisfied the criteria of all other subjects in the study (i.e. no Parkinson's, attended the same university, had a college entrance exam, etc).