One example of a measurement effect is the observer effect. Experimenter EffectsĮarlier we discussed measurement effects, defined as an effect on the data due to the act of measurement itself. An experiment in which both subjects and experimenters are kept "blind" about which group gets the real treatment is called a double-blind design (discussed below). The experimenter may be aware of which they are getting. The subjects are blind to which treatment they are receiving. That equalizes it between the groups (controls the variable of belief) removing belief in treatment as a confounded variable.Īn two-group experimental design in which subjects do not know whether they receive a placebo treatment or a real treatment is called a single-blind design. Both groups should experience an equal placebo effect. If both groups think they are receiving a genuine treatment, then belief is not a difference between groups. An experimental control is a procedure that removes such an unwanted difference, sometimes by holding a variable steady, sometimes by equalizing it between groups. Remember a confounded variable is an unwanted difference between groups. A researcher tries to create a placebo effect in the control group to equalize the placebo effect in the two groups. If it sounds wrong to you, study this concept until you understand it. The correct answer is "c." To some students, that sounds wrong. Students have no trouble understanding this idea, yet many still miss this question:ġ) How do you control the placebo effect?Ī) give the control group an experimental treatmentī) give the experimental group a "sugar pill"Ĭ) create a placebo effect in the control group How is the placebo effect controlled in research? This way the researchers can tell if the medicine has any effect beyond the expected placebo effect, which should be present equally in both groups. The experimental group gets the real medicine, the control group gets the placebo.īoth groups think they are getting a real medicine. When testing the effects of a new medicine, researchers must give the control group a placebo: a realistic-looking fake that contains no active ingredient. What are placebo effects? Are they imaginary?
For example, if you wore a certain cologne which made you feel more attractive, you might act more attractive and be more attractive, even if the cologne had no effect. They are genuine changes produced by a person's knowledge or belief. Placebo effects, defined this way, are not imaginary. To most psychology researchers, the phrase now refers to any situation in which a person's belief in a treatment contributes to the effect of the treatment (Critelli & Neumann, 1984). However, the phrase placebo effect has come to mean much more. The word placebo sometimes refers to a sugar pill or fake medicine. A placebo (pronounced pluh-SEE-bo) is literally a "pleasing thing." Placebo Effectsīelieving in something often helps to make it work.
In the example on the previous page, the student could have eliminated his confounded variable (volume) by making sure the his recordings were recorded at exactly the same volume level. On some occasions, an experimenter controls a variable by holding it steady. How could the student have eliminated volume as a confounded variable in his research? If one can demonstrate there is no difference between groups on that variable, the variable is removed as a confound. Methodological control can be achieved, sometimes, by merely measuring a variable. But physical control over variables is not always necessary. They visualize a laboratory scientist holding some variable such as temperature steady. Most beginning students take the word control literally. What does the word "control" mean when used in the context of experimental design? This is called methodological control it means a variable is "ruled out" as a confounded variable by the logic of the experiment.
In one sense of the term, to control a variable is precisely to remove it as a confounded variable. For every confounded variable, there is a potential control.
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