single blind study to test effectivness of aspirin as pain relief
get 10 patients with pain... give half aspirin and half a placebo
doctor knows which is which, but patient does not.... in effect the patient is 'blind' as to which is the real medicine
if the patient cannot know which is which, it removes the possibility of the patients own expectations affecting the outcome
double blind study
same as above, but patients are assigned a numbered drug
doctor does not know which is placebo and which is aspirin, neither does patient, until tests are complete
in this way, the expectations of the doctor cannot confuse/ affect the patient
in effect the doctor is 'blind' and the patient is 'blind' = double blind