An experiment allows the researcher to control the situation being studied. Instead of being a passive recorder of what is going on, the researcher actively does something that he or she thinks will affect the subject’s behavior and then observes what happens. These procedures allow the experimenter to draw conclusions about cause and effect.

The aspect of an experiment situation manipulated or varied by the researcher is known as the independent variable. The reaction of the behavior that the researcher tries to predict- is the dependent variable. Every experiment has at least one independent and one dependent variable.

Everything about the experimental situation expects the independent variable is held constant, that is, it is kept the same for all subjects. Holding everything but the independent variable constant ensures that whatever happens is due to the researcher’s manipulation and nothing else. It allows you to rule out other interpretations.

Experiments usually require both an experimental condition and a comparison, or control condition. In the control condition, subjects are treated exactly like those in the experimental condition, expect they are not exposed to the same treatment, or manipulation of the independent variable. Without a control condition, you can’t be sure that the behavior you are interested in would not have occurred anyway, even without your manipulation.

To accomplish this we can use random assignment to place people in the groups. We might randomly give each person a number, then put those with even numbers in the experimental group and all those with odd numbers in the control group. At the beginning of the study, each subject will have the same probability as any other subject of being assigned to a given group.

Instead of having the control subjects refrain from ___, we will give them a placebo, fake treatment. Placebos often take the form of pills or injections containing no active ingredients

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