extraneous variables
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Extraneous variables are those variables that are unknown or unforeseen at the start of a study that has a bearing on the results of the study.
Methods used to control extraneous variables:
Making sure that the samples are random ensures that the extraneous variables are standardized across the different groups. This makes it so that the effect of the extraneous variable becomes reduced than in cases where the extraneous variable is present only in certain sections of the sample (Behi & Nolan, 1996). Randomization reduces the effect of extraneous variables best where the sample size is large.
Statistical control. Specific statistical tools can be used to control the effect of extraneous variables in a study (Behi & Nolan, 1996). One such tool is the analysis of covariance (ANOVA).
Matching the different groups of extraneous variables to ensure uniformity can help reduce the effect of the extraneous variable on the study (Behi & Nolan, 1996).
