I used MEGA5.0 for computing MER for my dataset. the rates were computed based on JTT with an account of invariant sites model using 2 gamma categories for all positions in the alignment. these are scaled to 1 and sites showing rates >1 are suggested to be fast evolving. I wanted to understand the mathematical basis of this calculation and to infer if these are statistically significant. is there P value or standard deviation computed for this analyses? if yes how to I get this information.