# Data Analysis Resource Center

## "Exact" P values for multiple comparisons tests after ANOVA

The #1 suggestion we've heard from scientists to improve Prism 5.

The phrase "exact P value" can be interpreted in several ways, and Prism 6 offers two approaches.

Following Bonferroni, Tukey or Dunnet multiple comparisons testing, Prism 6 can compute a multiplicity adjusted P value. For each comparison, this is the smallest significance level (applied to the entire family of comparisons) where this particular comparison would just barely be declared to be "statistically significant". An adjusted P value is an “exact P value” reported for each comparison. But the value of the adjusted P value depends on the number of comparisons you are making, and on the data for all the comparisons.

The second approach Prism 6 uses to report "exact P values" is the unprotected Fishers Least Significant Difference (LSD)

## Statistics Guide

The GraphPad Statistics Guide is both a guide to doing statistical analyses with GraphPad Prism 6, and a concise review of statistical principles, emphasizing clear explanations with very little math.

Selected topics:

Go to the Statistics Guide

## Curve Fitting Guide

The GraphPad Curve Fitting Guide is both a  guide to fitting curves (and lines) with GraphPad Prism 6, and a concise nonmathematical explanation of the principles of linear and nonlinear regression.

Go to the Curve Fitting Guide