Which definition best describes a control in an experiment?

Select one:

It is a part of your experiment that changes.

It is a statement that sums up your results for your experiment.

It is a part of your experiment that doesn't change.

It is your explanation for the change that occurs in your experiment.

When possible, scientists test their hypotheses using controlled experiments. A controlled experiment is a scientific test done under controlled conditions, meaning that just one (or a few) factors are changed at a time, while all others are kept constant. We'll look closely at controlled experiments in the next section.

In some cases, there is no good way to test a hypothesis using a controlled experiment (for practical or ethical reasons). In that case, a scientist may test a hypothesis by making predictions about patterns that should be seen in nature if the hypothesis is correct. Then, she or he can collect data to see if the pattern is actually there.