# Overview for 2 Variances

Use 2 Variances to do the following:
• Determine whether the variances or the standard deviations of two groups differ.
• Calculate a range of values that is likely to include the population ratio of the variances or the standard deviations of the two groups.

For example, a quality engineer at an automobile manufacturer wants to compare the variance in the diameters of the camshafts produced for two different vendors. If the variances from the two vendors are different, the engineer uses the confidence interval to determine whether the difference is practically significant.

2 Variances is useful for quality improvement situations: you can use this test to compare the variance within subgroups to the variance between subgroups. Also, you can use this test to compare the process variance before and after you implement a quality improvement program.

## Where to find this analysis

• Mac: Statistics > 2-Sample Inference > Variances
• PC: STATISTICS > Two Samples > Variances
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