Bonferroni Correction

In statistics, the Bonferroni correction is a method used to counteract the problem of multiple comparisons. It is considered the simplest and most conservative method to control the familywise error rate.

Calculation
To calculate the new significance cut off point for comparisons, take the significance cutoff which was initially being used (p = .05) and divide it by the number of tests being run (3).

Example
Say you are comparing the means of three groups using an ANOVA, using a p = .05 cutoff for significance. Ad-hoc tests between the three groups should use a new significance cut off of p = .017 since .005/3 = .017.