Lecture
The occurrence of accompanying confoundings is related to the very way in which the independent variable is set, the recording of the dependent variable, or the actualization of the basic variable under study together with another basic process.
Accompanying confoundings are distinguished by the inherent connection of the confounding variable with the methodological conditions for controlling the variables or with other variables.
The general control scheme implies actualizing the active level of the accompanying variable in all experimental and control conditions.
In the general scheme for controlling accompanying confoundings, the place of the second (accompanying) variable may be occupied by various factors, always related to the way the independent variable is set.
An experimental design with control of an accompanying confounding.
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Accompanying variable |
Independent variable |
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Active level |
Inactive level |
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Constantly active level |
Experimental condition |
Control condition |
This scheme makes it possible to evaluate the placebo effect (the inactive level of the independent variable here includes an empty trial).
The use of a placebo is especially effective for the purpose of ensuring control when studying the effectiveness of interventions in cases where the very fact of administering the intervention may have an effect on the dependent variable.
(A cognitive model of the placebo: changes in emotional states relating to the goals of approach (a better state) – avoidance (of symptoms)).
Example: the effect of a physician's recommendation as a placebo (a 25% difference between different groups)
Control by means of factorial schemes.
In planning, such schemes are usually aimed at more clearly separating the basic processes underlying the influence of the independent variable, with an attempt to isolate the procedural effect of setting it from the causal influence under study.
An example given by Gottsdanker: Gaffan's experiment with monkeys and a severed fornix.
Hypothesis: severing the brain affects the deterioration of memory: in this case recognition, rather than association, is impaired. The experimental group consisted of monkeys with a severed fornix in the brain; the control group had an intact fornix. In order to rule out the influence of the accompanying variable on the differences – namely, the influence of the trepanation of the brain itself during the operation to sever the fornix on the deterioration of the animal's memory – the trepanation was performed on all the monkeys. That is, the accompanying variable is set in all conditions, and the differences should ultimately be due solely to the influence of the independent variable.
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