I have a trial with 8 groups. Each group experienced one of two treatments – four groups got treatment A & 4 got B. Within each group, the dependent variable was measured 4 times.
Unfortunately, the dependent variable is not normally distributed (or anywhere close). Given the repeated measures, I cannot therefore perform a Mann Whitney test on the 32 measurements I have. I could mean the 4 measures within each group & perform a Mann-Whitney on the means, but I have seen some suggestions of calculating ranks & performing multilevel modelling on those ranks.
Do you think that is appropriate?
If so, would:
MIXED rank_d BY Treatment Group
/CRITERIA=CIN(95) MXITER(100) MXSTEP(10) SCORING(1) SINGULAR(0.000000000001) HCONVERGE(0, ABSOLUTE) LCONVERGE(0, ABSOLUTE) PCONVERGE(0.000001, ABSOLUTE)
/FIXED=Treatment | SSTYPE(3)
/METHOD=REML
/RANDOM=Group | COVTYPE(VC).
be an appropriate analysis in SPSS?
Best Answer
GENLINMIXED with a Gamma distribution would be one way to look at this.