A mineral supplement designed to prevent the flu was given to two groups of people during a scientific study. Dosages of the supplement were measured in milligrams per day, as shown in the table below.
Supplement Dosages
Dosage
Group
(mg/day)
A
100
B
200
After 10 weeks, neither group reported a case of the flu. What is a procedure that would have made the outcome
of this study more valid?
A) test the supplement on both groups for 5 weeks instead of 10 weeks
B) test a third group that does not receive the supplement
C) test a third group that receives 150 mg the supplement
D) test only one group with 200 mg of the supplement