Psychology -> Placebo effect and experimenter effect: single-blind and double-blind procedure
Placebo effect and experimenter effect: single-blind and double-blind procedure
Placebo effect - IMAGE
A placebo effect is when there are changes in the subjects' behaviour caused by the belief that they received an active drug or treatment when, in fact, the drug was a neutral substance. This inert or neutral 'treatment' is called a placebo and is used to equalise the expectations of the control and experimental groups. For example, if you wanted to test the effects of a new drug which was supposed to improve memory, you could have two groups. The experimental group would be given the drug in tablet form and the control group would be given tablets that looked the same as those received by the experimental group, except that they contained glucose (a placebo). Both groups would then be tested on a memory task. In this experiment, the subjects feel that they have been treated equally and any difference in the groups would most likely be due to the drug.
In another experiment, three groups could be tested where group one was given the drug, group two, a placebo, and group three nothing. If the results of groups one and two were very similar and much higher than group three, then this is an example of a placebo effect.
• Experimenter effect
This is the way in which an experimenter might influence the outcome of an experiment without realising that he or she is doing so. In order to minimise subject or experimenter effects, researchers design single and double-blind experiments.
In a single-blind experiment, the subjects do not know whether they are in the control group or experimental group condition. This prevents the subjects' knowledge or expectations of the experiment impacting on the results.
In a double-blind experiment, the data collection is carried out by a third party who is told what to do but has no knowledge of the expected outcomes or which group is which. Thus neither the subjects nor the experimenter can bias the experiment.
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