Key Concepts

• A test of two variances may be one-tailed or two-tailed.
• The conditions for an F test on two variances are:
  • The populations from which the two samples are drawn are normally distributed.
  • The two populations are independent of each other.
• The test statistic is based on the assumption that the variances are equal. It is [latex]F = \frac{(S_1)^2}{(S_2)^2}[/latex].

Glossary

Variance: mean of the squared deviations from the mean; the square of the standard deviation. For a set of data, a deviation can be represented as [latex]x- \overline{x}[/latex] where [latex]x[/latex] is a value of the data and [latex]\overline{x}[/latex] is the sample mean. The sample variance is equal to the sum of the squares of the deviations divided by the difference between the sample size and one.