A new cream was developed to reduce the irritation caused by poison ivy. To test the effectiveness,
researchers placed an ad online asking for volunteers
to participate in the study. One hundred subjects
replied and were informed that one group would
receive the new cream and the other would receive a
cream with no active ingredient. All 100 subjects were
exposed to poison ivy. Fifty were then randomly
assigned to the group with the new cream, and 50
were randomly assigned to the group with the cream
with no active ingredient. After three days, the
subjects' level of irritation was measured.