Question

to determine if a drug has an effect on patient illness, a researcher gives the drug to 100 patients and gives a placebo to another group of 100 patients. what type of study is this?

Explanation:

This is an experiment as it involves manipulating a variable (giving drug or placebo) and observing the effect on patient illness. There are two groups - an experimental group getting the drug and a control group getting the placebo.

Answer:

Experiment