Hello,
I’m testing whether two empirical distributions are identical or not. I have a group of people with two observations for the variable ‘EKC’, ‘before’ and ‘after’ some intervention. I’m using K-S for the comparison of both distributions. Additionally, observations come from a national survey, so each individual contains a survey weight (i.e. weight) to produce national estimates. See code below:
ods graphics on;
proc npar1way data = dat edf;
freq weight;
class time;
var ekc;
ods output KS2Stats=ks;
run;
Notice in the table below, that both distribution are very similar (almost identical).
Percentiles
Before
After
Differences
% change
100% Max
3289.1
3279.5
-9.6
0.3
99%
2443.7
2436.6
-7.1
0.3
95%
2180.5
2173.5
-6.9
0.3
90%
2047.3
2040.8
-6.4
0.3
75% Q3
1838.8
1832.6
-6.2
0.3
50% Median
1623.3
1617.6
-5.6
0.3
25% Q1
1427.8
1422.7
-5.2
0.4
10%
1271.8
1266.9
-4.9
0.4
5%
1187.6
1182.7
-4.9
0.4
1%
1029.4
1024.9
-4.6
0.4
0% Min
642.3
638.4
-3.9
0.6
Nevertheless, the K-S for the comparison of the two samples suggest the both distributions are different ((Pr > KSa) <.0001).
I’m not sure how the fact that both empirical distributions are not independent (note they come from the same groups of individuals before and after some intervention) can affect the test. If so, can you please suggest an alternative valid test?
Thanks a lot,
A.G.
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