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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.

A simple experiment should have only one independent variable. All other factors that could have an effect on the outcome of the experiment must be controlled or held constant.

An experiment we're actively putting people or things into a control versus treatment group. In the treatment group, you put the people and you usually would want to randomly select people into the …

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One challenge when researching whether holding elected office changes a person’s behavior is the problem of ensuring that the experiment has an appropriate control group.

Ideally, the subjects in both experiments and observational studies should be randomly chosen from the population of interest. However, in an experiment, it is also beneficial to randomly assign subjects to …

In an observational study, we measure or survey members of a sample without trying to affect them. In a controlled experiment, we assign people or things to groups and apply some treatment to one of the …

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To avoid errors, researchers may randomly divide subjects into control and experimental groups. Both groups should receive a treatment, like a pill (real or placebo), to counteract the placebo effect.