Specify the alpha level for Analysis of Means

In Alpha level, enter a value for the error rate, or alpha (denoted as α). Usually, an alpha level of 0.05 works well. This alpha level indicates a 5% risk of concluding that a difference exists when there is no actual difference.

The decision lines on the analysis of means chart are based on an experiment-wide error rate, similar to a family error rate you can use when making pairwise comparisons in ANOVA.