Question

A dental student wants to test if fluoride is an effective additive against tooth decay. The student studies tooth decay in a population of people who live in neighborhoods supplied with fluoridated water. This student would like to ask whether access to fluoridated water prevents tooth decay. What would be an effective control group to ask this question?

a. Individuals who have fluoride added to their toothpaste but not their water.
b. Individuals with access to differing amounts of fluoride in the water.
c. Individuals with access to water with no fluoride added.
d. Individuals with access to fluoridated water.

Answer 1

Answer:

c. Individuals with access to water with no fluoride added.

Explanation:

In order to conduct an effective control group and make a reproducible research, only one variable (in this case the fluoridated water) should be modified at the time.  

The option b. Individuals with access to differing amounts of fluoride in the water could be selected if the reseach would evaluate the different levels of tooth decay.