Compare non-normally distributed, paired mean scores by independent group

[eap]

I wish to test for significance among paired pre-test & a single posttest score (dependent variables) and categorical age (Independent variable). The dependent variables are non-normally distributed. I created a new dependent variable 'MEANDIFF' [posttest score - pre-test score] and used a nonparametric method:

proc npar1way data=have wilcoxon;

class agegrp;

var MEANDIFF;

run;

Factor	Pretest Score	Posttest Score	p-value
			p-value here
<18	54.2	74.3
18-34	58.6	75.8
35-54	57.1	80.2

I get an overall p-value but am not sure if it's statistically sound to do this. Should I just report medians and (IQRs) and not report a p-value?

Any insight?

[PGStats · Accepted solution]

You should be testing MEANDIFF for location, i.e. is it significantly greater or less than zero, with the sign or signed rank test in proc univariate. See example

https://documentation.sas.com/?cdcId=pgmsascdc&cdcVersion=9.4_3.5&docsetId=procstat&docsetTarget=pro...