topic Looking for better approach to do ttest in Statistical Procedures

Looking for better approach to do ttest

Madhu6 — Sat, 18 Jun 2022 04:29:22 GMT

Hello Everyone,

I have two datasets Pr_table5 (test) and C_table5 (control).

Each table consists of CD3 tested on different time intervals (day 0 day3 day7 day14 day30) with different n on each day. For example, day0 N is 63, and day30 N is 50

I am calculating a t-test comparing Pr_table5 and C_table5 to get the following table:

T-Tests
Variable	Method	Variances	DF	t Value	Pr > \|t\|
mean	Pooled	Equal	XX	XX	XX
mean	Satterthwaite	Unequal	XX	XX	XX

So I calculated the mean for Pr_table5 (mean of day0, mean of day3...) and c_table5 (mean of day0, mean of day3...) and dropped n min max std so that it will have only mean from table1 and table 2.

proc means data = Pr_table5 noprint;
output out = a(drop = _type_ _freq_ );
run;
proc transpose data = a out = a (drop  = n min max std ) ;
id _STAT_;
run;

proc means data = c_table5 noprint;
output out = b(drop = _type_ _freq_ );
run;

proc transpose data = b out = b (drop  = n min max std ) ;
id _STAT_;
run;

Then I merged two tables (combo) which contain means from two tables.

data combo_a;
set a ;
_name_ = 'mean_a';
run;
data combo_b;
set b ;
_name_ = 'mean_b';
run;
data combo;
set combo_a combo_b;
run;

Next, I did a t-test.

proc means data=combo noprint;
var mean;
by _name_;
output out=new_combo;
run;
proc ttest data=new_combo nobyvar;
class _name_;
var mean;
run;

Please let me know if there is a better approach, from both a statistical and programming point of view.

Thank you,
Madhu

Re: Looking for better approach to do ttest

Reeza — Sun, 19 Jun 2022 03:01:43 GMT

Can you do it directly on the raw data? SAS can analyze the difference between summarized data but this seems a bit weird to me.

Are you certain the code posted works correctly because it seems like you'd only have a single observation and PROC TTEST expects multiple. Or it expects the more data from PROC MEANS, specifically the N and STD usually.

data combo;
set pr_table5 c_table5 (indsname=source);
dset = source;
run;

*really don't think you need this step but if you think you do for some reason;
proc means data=combo nway stackods mean;
class dset;
ods output summary = combo_means;
run;

proc ttest data=combo_means;
class dset;
var mean;
run;

Here's an example of how to do PROC TTEST on raw data.

https://stats.oarc.ucla.edu/sas/modules/an-overview-of-statistical-tests-in-sas/

If you have repeated measures as well, is there a reason you're aren't using a repeated measures type of analysis instead of just PROC TTEST?

https://documentation.sas.com/doc/en/statug/15.2/statug_glm_examples07.htm

Re: help needed with using proc glm

Madhu6 — Wed, 22 Jun 2022 00:49:23 GMT

Hello Reeza and everyone,

Thank you so much for your input.

Please see the attachments for control and test datasets. Here is the code to import them.

proc import out=Control datafile='C:\Users\SDSP\Desktop\Control.txt';
run;
proc import out=Test datafile='C:\Users\SDSP\Desktop\Test.txt';
run;

Treatment : '1' is control and '2' is test.

Then I merged the two tables by treatment.

data final_table;
merge control Test;
by Treatment;
run;

Now I want to compare the two groups (control and test) and see if they are different:

I used the below code (I am sure it is not correct). Can someone please help me with this

proc glm;
class Treatment;
model Day0--Day720 =
Treatment */ nouni;
repeated 8 (0 3 7 15 30 90 180 360 720) polynomial / summary printe;
run;

Thank you,

Madhu