Trisha wants to find out whether a certain pesticide is carcinogenic to amphibians. Trisha is designing an experiment to test the problem. She is planning on exposing frogs of the same species to different amounts of the pesticide. Should Trisha include a control group in her experiment? A. No, Trisha will not need a control group because if any frogs develop cancer, it will be obvious that the pesticide is the cause. B. No, a control group is not necessary because Trisha will be testing different exposure rates of the pesticide. C. Yes, Trisha should have a group of frogs in her experiment that are not exposed to any pesticide at all. D. Yes, Trisha should use a different species of frogs as her control group.

The election of a control group is essential in an experiment. Its principal purpose is to allow the discrimination of the results obtained by the treatment in the study (in this case, the effect of pesticide) from the results that might be a consequence of other factors. The control group must be selected from the same population of the treatment group. All the groups must be similar in every variable that might influence the results, except for the study treatment.

Control group: Frogs that are not exposed to any pesticide

Treatment one: Frogs exposed to a certain concentration of pesticide

Treatment two: Frogs exposed to an increased concentration of pesticides ...

And so, the number of treatment groups will depend on the different concentrations of pesticides Trisha wants to study.

All groups must belong to the same population and of course, to the same species. They must also be exposed to the same variables, excepting for the pesticide variable.