Okay, here's the scenario: We have a study with a negative control group, a solvent control group, and 5 treated groups. The statistical protocol calls for: 1) pooling the control groups for comparison to the treated groups, and 2) comparing the treated groups to the solvent control alone. The first thing we do is run a Shapiro-Wilk's test for normality and Bartlett's for homogeneity, then move on to ANOVA and Bonferroni. This is done using the entire data set with pooled controls. For the next analysis (to solvent control only), the negative control data is removed from the data set; so now we've got the solvent control and 5 treated groups. The analysis is done by going directly to an ANOVA, with no Shapiro-Wilk's or Bartlett's to check for normality and homogeneity. The reasoning is that if the data set is normal and homogeneous with the negative control data included, then it is not necessary to check it again after this data is removed from the set; it will be normal and homogeneous without it too. Is this legit? I have my doubts, but the powers that be are telling me, "Ahhh..no problem". Opinions? Thanks.