topic Help with running wilcoxin signed rank test on two (not independent) variables in SAS Programming

Help with running wilcoxin signed rank test on two (not independent) variables

jessho — Thu, 23 Jan 2020 21:35:47 GMT

Hi-

I have two non-normally distributed variables, RA_Opening and RA_Vasoactive, which are not independent. I am trying to run a non-parametric test on them--wilcoxin signed rank test.

What is the easiest way to do this? Should I just create a new variable, RA_Change, for difference between the two and run proc univariate or is there another way?

Data per below:

RA_Opening	RA_Vasoactive
21	8
15	14
15	18
8	6
28	9
18	12
30	15
10	4
6	4
15	5
27	11
15
13	8
14	4
10	2
8	8
11	14
18	16
19	8
12	9
16	8
12	12
13	14

Re: Help with running wilcoxin signed rank test on two (not independent) variables

ballardw — Thu, 23 Jan 2020 21:48:22 GMT

By not independent do you mean that your RA_Vasoactive values are expected to change in a certain manner with changes in the RA_Opening value (or vice versa)?

That would look more like a regression problem.

Otherwise the Univariate approach seem like what you want with an added variable for the difference if the values are paired

Re: Help with running wilcoxin signed rank test on two (not independent) variables

Rick_SAS — Fri, 24 Jan 2020 15:15:26 GMT

I assume that these are paired observations before and after some time period or event. You can compute the difference between the values and test whether the mean (or median) difference is significantly different from 0:

data Have;
input RA_Opening	RA_Vasoactive;
diff = RA_Opening - RA_Vasoactive;
datalines;
21	8
15	14
15	18
8	6
28	9
18	12
30	15
10	4
6	4
15	5
27	11
15	 .
13	8
14	4
10	2
8	8
11	14
18	16
19	8
12	9
16	8
12	12
13	14
;
proc univariate data=Have mu0=0 loccount;
   var diff;
   histogram diff / href=0;
   ods select TestsForLocation LocationCounts Histogram;
run;

In this case, 17/20 differences are greater than 0, so the signed rank test rejects the null hypothesis that the difference is 0.