topic Re: mann whitney for two sample test in Statistical Procedures

mann whitney for two sample test

karora1 — Thu, 15 Nov 2018 19:37:00 GMT

I was going to run a two sample ttest for a project i am working on that has 111 in one group and 121 in the other. However after exploring the data one of the groups appears to have a non-normal distribution. I wanted to run a man whitney non parametric test and discovered this code for SAS.

proc NPAR1WAY data=IVPO_final wilcoxon;
	title "Nonparametric test to compare Age";
	class convert_total;
	var Age_on_Admission;
	exact wilcoxon;
   run;

However, when i run it i get the warning that it will take a lot of time and memory. I have yet to see the results of the analysis. Is there a better way to run this type of analysis or a different code to use. etc.?

Re: mann whitney for two sample test

ballardw — Thu, 15 Nov 2018 21:39:59 GMT

Are you sure you need "exact" tests?

You might consider adding the option MAXTIME= such as

proc NPAR1WAY data=IVPO_final wilcoxon;
	title "Nonparametric test to compare Age";
	class convert_total;
	var Age_on_Admission;
	exact Wilcoxon /maxtime=60;
   run;

which will limit the exact test calculations to about 60 seconds and terminate if it takes much longer than that. So set a time limit you are comfortable with and take a coffee break or such.

Re: mann whitney for two sample test

PGStats — Thu, 15 Nov 2018 21:52:46 GMT

Go for Monte-Carlo estimation with

exact wilcoxon / MC;