The control group is a group that is used as the baseline, to see what happens under normal conditions. The control group does not get any experimental treatment. In a drug trial, the control group gets a fake pill.

The experimental group gets the experimental treatment (the real pill), so you can test whether the drug works.

The independent variable is the one you control. Here, you are choosing whether people get a fake pill or a real pill.

The dependent variable is the one you measure, as an output of the independent variable (i.e., the value of the dependent variable *depends* on the value of the independent variable). You measure the health of both the control and experimental groups as the dependent variable.

If you did the experiment without a control group and saw an improvement in the health of people taking your drug, you might think the drug is working. But if you have a control group that didn’t get the drug and THEIR health also improves, then you know the drug is useless.

If, on the other hand, the health of the experimental group is statistically better than the health of the control group, that suggests that the drug treatment (the independent variable) works.

The twins who did not get tomato juice are referred to as the control group, because nothing has changed in their environment. (You use twins in this kind of experiment because both the control twin and the experimental twin have the same genetic background and live in identical surroundings).

The twin that gets the tomato juice is in the experimental group.

Dependent variables would be something that is related to what you are doing – in this case, monitoring whether the hair turns red or not. Independent variables are other things that might happen – such as one set of twins gaining weight or growing an extra two inches.

Does that help?