Determine whether the follow descriptions correspond to an observational study (OS), a controlled experiment (CE), or a double blind experiment (DBE). Write the abbreviations above as your answers. (without the parenthesis)

(a)A doctor gives half of his/her patients in a study a treatment and the other half a placebo, but the patients do not know which they received.

answer:___________

(b)A therapist compiles information on his/her patients who have survived child abuse to explain the effects of child abuse on adult survivors.

answer:_____________

(c)A new study examines the effects of regular exercise on child obesity by taking a survey of 500 children on their weight and exercise habits.

answer:_______________