Changes in Dunnett's test between Prism versions

The Dunnett's test relies on tabulated critical values of q, which are not trivial to compute.

Prism 7.05 and 7.0e improve the calculation of P values and confidence intervals when sample size is unequal. 

Prism 5 uses tables for significance levels of 5%, 1% and 0.1%. The tables for 5% and 1% are widely available, but the table for 0.1% is not. We use this table created by SAS. These tables have five digits of precision. 

Prism 4 uses tables for significance levels of 5% and 1% only. So Prism 4 can report a P value less than 0.01, but not less than 0.001. The tables used for Prism 4 only have 2-3 digits of precision. 

Prism 3.02, 3.03, 3.0a, 3.0b:   The same as Prism 4. 

Prism 3.00, 3.01, 3.0a, 3.0b: Incorrectly reported  "P<0.001" when the P value was really less than 0.01, and never reported "P<0.01".