Pearson offered one way to statistically control certain variables in 1895 with part correlation, which is used with multiple correlation only and thus involves three or more variables. It is the correlation between the dependent variable and one of the independent variables after the researcher statistically removes the influence of one of the other independent variables from the first independent variable. Thus, the researcher can mathematically isolate the variable when it cannot be experimentally isolated. The statistician is essentially treating the item as if one of the variables doesn’t
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