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I am looking to determine whether patient's total number of prescriptions (RxTotal) differs by membership within 3 possible groups (ie run an ANOVA), and if so, to determine which groups differ (ie run multiple comparisons). My data is non-normal (Shapiro Wilk p<.0001) and the groups have unequal variances (Levene p<.0001). My group Ns are 113, 202, and 90. I understand that ANOVA is fairly robust against violations of normality and HOV as long as each group has equal Ns. I do not know if the Ns of my 3 groups could possibly be considered "equal" so I have chosen to go with using Welch's F statistic (p<.0001), although I am open to feedback to take other routes. I have read that the Games-Howell multiple comparisons test works well with HOV violations, and that it is the Welch's equivalent of the Tukey post hoc test. I have searched at length and cannot figure out what the syntax would be for running Games-Howell multiple comparisons tests in SAS. Is this perhaps because it requires a macro, or is there an option built into a standard SAS procedure that I have not found?

This is my syntax for running the Welch ANOVA, and the Tukey post hoc tests (which I am inclined not to use):

proc glm data=cutoffs1;
class group;
model rxtotal = group;
means group / welch tukey;
run;

Thank you!

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  • $\begingroup$ Unless the counts of total prescriptions are quite high, I'd probably use a count regression, either Poisson or negative binomial. $\endgroup$
    – Peter Flom
    Sep 6, 2023 at 18:54
  • $\begingroup$ Thank you so much. I would like to run multiple comparisons between all 3 groups on the count outcome, not just two groups compared to a reference group. Would there be an accepted way of using a Poisson regression approach that would allow for that? Thank you $\endgroup$
    – L.S.
    Sep 13, 2023 at 15:22
  • $\begingroup$ The same methods as with PROC GLM should work, I believe. $\endgroup$
    – Peter Flom
    Sep 13, 2023 at 16:03

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