A student is conducting their science experiment on the effect of caffeine on dogs. He has 3 groups of test subjects. The 1st group of dogs receives plain water. The 2nd group of dogs receives 10 mg
of caffeine each, and the 3rd group receives 50 mg of caffeine each. He will measure their activity
levels by recording how long each dog runs without stopping, after giving them the pills. What is the
control group in this experiment?
A. How the caffeine is given to the dogs.
B. The dogs that receive water.
C. The dogs that receive 10 mg of caffeine.
D. How the activity levels are measured.

The control group might be defined as the one that does not receive any treatment -meaning the independent variable-. So in this example, the control group are the dogs that receive water (option B). These dogs do not get caffein, which is the independent variable.

During an experiment the researcher compares at least two groups: a control group and an experimental group. Both groups are composed of individuals coming from the same population, so they are identical in all aspects except for the independent variables.

The control group is used to identify any other factors influencing the results obtained in the study, apart from the modified variables of the treatment. The independent variable keeps constant in the control group. The experimental group receives the treatment. The researcher voluntarily changes the values of the independent variable to observe how it affects the individuals subjected. There can be several experimental groups.

So, in the exposed example, the population is composed of dogs. From this population, the researcher selects one control group and two experimental groups. The independent variable in this study is the amount of caffeine provided to dogs.

the control group ⇒ is the first group of dogs that only get water, the experimental groups ⇒ are the second and third groups of dogs that get 10 mg and 50 mg of caffeine each, respectively.

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