Control group?

Question

What is the value of having a control group in an experiment?

Answer 1

The point of having a control is such that if you have an experiment with two groups, and the only difference between the two groups is your experimental variable (the one without the variable is your control), you can know that any differences between the two groups are due only to your experimental variable. It's a way of keeping science "honest".

Answer 2

The purpose of a control group is to show that the dependent variable(DV) is CAUSED by the independent variable(IV). For example, in order to PROVE that rhodium causes cancer you need 2 groups of rats. One group gets 5 cc rhodium shots, the other group does gets 5 cc saline shots. The group getting saline shots is the control group. Everything is the same between the 2 groups EXCEPT the liquid in their shots. If the DV(cancer rates) differs significantly between the control group (rats getting saline shots) and the experimental group (rats getting rhodium shots) we can deduct that the IV (rhodium) caused the DV (cancer).
By having the control group, researchers show that the only way to explain the differences between 2 groups is that the IV caused the differences.

So, in short, the value of a control group is that it allows researchers to make a CAUSAL CLAIM.

Answer 3

You can determine the "normal" base for your test. If checking if something can cause another thing to be abnormal, this is vital.