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Experimental and control groups and their purpose in experimental psychological and pedagogical research
An experimental group is a group that is directly exposed to experimental effects in the research process. The experimental group consists of individuals who will be exposed to an independent variable , or stimulus.
The control group is defined as a group of subjects, similar to the experimental group, which is placed in the same conditions as the experimental one, except that the subjects in it are not exposed to the experimental effect (independent variable).
The experimental and control groups should be almost identical. The identity of the experimental and control groups is achieved in three ways.
The first method is pairwise alignment of objects according to significant variables established before the experimental operations. For each selected test subject, a different test subject with the same combination of relevant characteristics is selected as part of the control group. As a result, two groups arise that are identical in terms of characteristics that could affect their reaction in the experiment.
The second , more accessible , method of group alignment is based on equalization of frequency distributions , and not each pair individually. The subjects are divided into groups in such a way as to guarantee the presence in each group of the same average characteristics and the same distribution of each characteristic. For example, an experimenter provides a 30 percent share of subjects with higher education in both groups. Similar alignments are carried out on other grounds, and individual subjects are no longer controlled. Of course, in this case, high similarities between groups are not achieved, but the recruitment of groups is much easier.
The third method of forming groups is more flexible in comparison with the exact selection of matches. This is a randomization method. A test subject selected from the list of all suitable subjects is included in the group through some random process, for example, using a table of random numbers. Randomization has a great advantage, creating a feeling of confidence in us that all our groups are similar to each other in all respects, and not only in terms of variables that we consider relevant for the experiment, because when selecting a large number of subjects, random distribution among groups ensures the neutralization of differences between subjects.
The selected experimental group is intended to establish reliable statistical dependencies between the studied variables , and control groups - in order to, by comparing the results obtained in them with those established in the experimental group, reject alternative causal explanations of the revealed statistical dependence . In the simplest case of the implementation of this scheme, one experimental and one control group are taken.
In the experimental group , a variable is singled out and purposefully changed , which is considered as the probable cause of the explained phenomenon, but nothing happens in the control group. At the end of the experiment, changes that are evaluated and compared among themselves, which occurred in the experimental and control groups with another variable, are dependent, and if it turns out that in the experimental group these changes are greater than in the control group, it is concluded that their true cause is it is the action of the independent variable that took place in the experimental group.
The value of the dependent variable in each group is measured before the stimulus exposure during the so-called pretest and then again after the experimental group was exposed to the stimulus during posttest . The conclusion about the influence of the stimulus (independent variable) is made on the basis of a comparison of the estimates of the preliminary test and the control test for each group. The greater the difference in values between the preliminary test and the control test in each group, the more influence is attributed to an independent variable.
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