Enter your data for Power and Sample Size for 2 Variances

Stat > Power and Sample Size > 2 Variances

Complete the following steps to specify the data for the power and sample size calculation.

  1. From the drop-down, you can specify whether to analyze a ratio of standard deviations or a ratio of variances.
  2. Specify values for two of the following power function variables. Leave the variable that you want to calculate blank.
    • Sample sizes: Enter the number of observations for each group. For example, enter 50 to indicate that you will collect 50 observations for each of the two groups. To assess the effect of different sample sizes, enter multiple values. Larger sample sizes give the test more power to detect a difference.

      If you enter multiple values into a field, separate the values with a space. You can also use shorthand notation to indicate multiple values. For example, you can enter 10:40/5 to indicate sample sizes from 10 to 40 in increments of 5.

    • Ratios: Enter one or more values to specify the difference that you want to detect between two groups. Usually, you enter the smallest ratio that has practical consequences for your application. A ratio of 1 suggests equality between the groups.

    • Power values: Enter one or more values to specify the probability that the test detects a difference between the two variances or standard deviations when a difference actually exists. Common values are 0.8 and 0.9. For example, analysts enter 0.9 because they want a 90% chance that the test will detect an important difference between the variance of two assembly lines when a difference actually exists.