Variance Analysis Ratio VAR

A plot of the Variance Analysis Ratio may be used to select a transform of the response. Transforms are sometimes of value in stabilizing the data variance from a fitted model; a stable variance is more uniform over the range of the data.

If the error is unbiased, the slope of the line fitted to the Standard Deviation of the subgroup variances plotted against the subgroup means is λ, a slope constant for that factor (Refer to General References, Box, Hunter, Hunter, 1978, p.232).

The Table below provides a suggested variance stabilizing transform for some values of the VAR. For a given set of data replicated at set conditions, the VAR is estimated as the slope of the line when plotting the log of the means (x-axis) versus the log of the standard deviations (y-axis) for each set of replicated data.

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