topic Re: Matched paired or independent two groups??? in Statistical Procedures

Matched paired or independent two groups???

DJ — Thu, 14 Jun 2012 17:15:41 GMT

Hello friends,

I have a question regarding selection of statistical test. Here is the situation: we have two treatments A & B and would like to compare differences between A & B. We have 100samples, we made two aliquots from each sample and applied both treatments. How should I treat this data - matched pair or independent two groups?

Which SAS procedure will work for me?

Thanks in advance.

Re: Matched paired or independent two groups???

PGStats — Thu, 14 Jun 2012 18:11:05 GMT

I would treat the data as matched pairs :

proc glimmix data=test plots=all;

class treat sampleId;

model x = treat / solution;

random intercept / subject=sampleId;

run;

look carefully at the residual plots for any pattern.

Re: Matched paired or independent two groups???

DJ — Thu, 14 Jun 2012 18:32:01 GMT

Hi PG,

Thanks for the prompt reply.

Is there any non-parametric test appropriate to this problem?
Thanks

Re: Matched paired or independent two groups???

PGStats — Thu, 14 Jun 2012 20:09:27 GMT

You could do a Wilcoxon signed ranks test on the difference between treatments (A-B) for each sample. It is available in PROC UNIVARIATE.

Re: Matched paired or independent two groups???

SteveDenham — Fri, 15 Jun 2012 11:50:29 GMT

I am very curious as to why the OP would want to do a non-parametric test. Are the response variables really non-normally distributed? If the response variable is a concentration, perhaps a lognormal distribution can be assumed, and the GLIMMIX approach appropriately modified with a dist= option. On the other hand, if there is a problem with responses being above or below limit of quantitation for the assay, I can understand wanting to move to a nonparametric test. However, if this is not the case, the detectable difference for the nonparametric test will be much larger than for the parametric test.

And of course, once those plots are examined, it may be really obvious why a nonparametric approach would be needed.

Steve Denham