topic Re: PROC TTEST compare two groups in SAS Programming

PROC TTEST compare two groups

Anita_n — Mon, 29 Nov 2021 11:16:14 GMT

Dear all,

Am trying to compare C-reactive protein (CRP) values of patients at visit1 and vist 2

I have table that looks like this :

Variable	VISIT	N	Mean	STD
CRP	1	300	3,64	1,19
CRP	2	148	1,95	0,93

I wish to compare the N value 148 at visit 2 with exactly 148 values at visit1. I think I can do this by selecting the pat_id with the 148values at visit2 and comparing that with exactly the same patients(with the same pat_id) in visit1

My question is how can I adjust my code to do that?

here is my code:

proc ttest data= myinfile plots=none;
class visit;
var CRP;
where visit in (1,2);
ods output ttests=ttest_CRP;
ods output Statistics=Stat_CRP;
run;

Re: PROC TTEST compare two groups

Ksharp — Mon, 29 Nov 2021 12:24:10 GMT

Check this example:

Re: PROC TTEST compare two groups

Reeza — Mon, 29 Nov 2021 17:01:47 GMT

Adding the link to that example, including the code.
https://documentation.sas.com/doc/en/pgmsascdc/9.4_3.3/statug/statug_ttest_examples01.htm

Re: PROC TTEST compare two groups

PaigeMiller — Mon, 29 Nov 2021 17:08:15 GMT

Before we show any code, could you clarify something here:

I wish to compare the N value 148 at visit 2 with exactly 148 values at visit1. I think I can do this by selecting the pat_id with the 148values at visit2 and comparing that with exactly the same patients(with the same pat_id) in visit1

If there are two measurements for each of the 148 patients, then you would want to do a paired t-test for these 148 patients. Is that what you have in mind?

Re: PROC TTEST compare two groups

Anita_n — Tue, 30 Nov 2021 09:42:03 GMT

@Ksharp @Reeza : Thanks for that.

@PaigeMiller Yes, that is approximately what I want. I think I will try that myself. Thanks