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How to test the interaction between strata and treatment groups in a mmrm model?

Robin_moon — Sun, 28 Apr 2024 09:22:42 GMT

I constructed a mmrm model as below:

 proc mixed data = have;
 class id treatment week strata;
 model chg = base treatment week treatment*week treatment*strata/ ddfm = KR;
 repeated week/ subject = id type = UN;
 lsmeans treatment*week/ cl alpha = 0.05 diff
 ods output Tests3=tests3 lsmeans=lsmeans diffs=diffs;
 run;

(1) id: represents the patient id;

(2) treatment: contains 2 group, "drug" and "placebo";

(3) chg: change from baseline of hba1c;

(4) base: the value of hba1c at baseline;

(5) week: contains 3 levels: "week8", "week16" and "week24"

(6 )strata: stratification based on the median of baseline hba1c, ie

group1=patients of those who have baseline hba1c <= median of baseline hba1c;

group2=patients of those who have baseline hba1c > median of baseline hba1c.

In general, I'd like to know how to the test the interaction between strata and treatment groups. I am not sure if I constructed the model in a right way because I looked at the results (as below), the values of Diffs in LS means were pretty close between strata, but p for interaction was significant. (The Diffs in LS means were got from the output file diffs, and the p for interaction were got from the output file test3.)

I also checked the Diffs in LS means of week8 and week16, the diffs in LS means were all pretty close between 2 strata, but the p for interaction were all significant (p-value < 0.0001). So I am not sure if I interpret the result in the right way. What data should look quite different if the p for interaction is statistically significant? Thanks.

Re: How to list all the datasets with same end in a simpler way?

Robin_moon — Sun, 28 Apr 2024 08:57:40 GMT

Thanks for sharing the link. So sad to hear from that. SAS has a shortcut for selecting variables with same prefix but not for suffix.

How to test the interaction between strata and treatment groups in a mmrm model?

Robin_moon — Sun, 28 Apr 2024 08:51:06 GMT

I performed a mmrm model as below:

 proc mixed data = have;
         class id treatment week strata;
         model chg = baseline treatment week treatment*week treatment*strata/ ddfm = KR;
         repeated week/ subject = id type = UN;
         lsmeans treatment*week/ cl alpha = 0.05 diff
         ods output Tests3=tests3 lsmeans=lsmeans diffs=diffs;
         run;

In the model:

(1) id: represents the patient id, ie 101,102,103....

(2) chg: represents the change from baseline of hba1c

(3) baseline: the value of hba1c at baseline

(4) treatment: contains 2 categories: "drug" and "placebo"

(5) week: contrains 3 levels: week8, week16, week24

(6) strata: represents the stratification by the median of hba1c at baseline, ie:

group1=patient of those who have hba1c at baseline <= median of hba1c at baseline;

group2=patient of those who have hba1c at baseline > median of hba1c at baseline.

In general, I'd like to test the interaction between strata and treatment, but I am not sure if I performed the test in the right way. Because I checked the results (as below), the column of "Diffs in LS means" were pretty close between strata, however the interaction p-value is statistically significant. (The values of Diffs in LS means were got from the output file diffs, and the p for interaction were got from the output file test3.)

I also checked the Diffs in LS means not only at week24, but also week 8 and week16, they all looked pretty close between strata. So did I interpret the data in a wrong way? Or did I perform the model in a wrong way? What data should look different if the p for interaction is significant? Thanks!

How to list all the datasets with same end in a simpler way?

Robin_moon — Fri, 26 Apr 2024 06:58:35 GMT

I saw a loop code the other day. And it generate files of output_&i (i.e. output_1, output_2,..., output_n). At the end, it row bind all the files as:

data all_results;
     set output_:;
run;

It seems that we could list files output_1, output_2, ... , output_n in a simple way by using ":" as output_:, so I tried to row bind my files that all end up with "_output" (i.e. 1_output, 2_output, 3_output) in a similar way:

data all_results;
    set :_output;
run;

But it failed. I'd like to know how to write the code in the right way. Thanks!

How to pass the time value to another variable?

Robin_moon — Thu, 20 Jan 2022 12:47:26 GMT

I have a column called startdate with time values, like:

30JUN1948:00:00:00.000

07JAN1967:00:00:00.000

01FEB1953:00:00:00.000

...

When I tried to pass the time value to a new variable called start, like this:

data want;
set data have;
start = startdate;
run;

The new column start looked like this:

-363052800

221443200

-218160000

...

I'd like to know how to pass the date time value to the new column with its original format? Thanks.

How to convert xpt file into sas file by xpt2loc?

Robin_moon — Wed, 19 Jan 2022 13:09:06 GMT

sI tried to convert two xpt file called "ae.xpt" and "se.xpt" into sas file called ae and se as well. The original file was saved at "D:\sdtm\data_xpt", and I want the converted sas file to be saved at "D:\sdtm\data_sas".

Here was my code, but it didn't work:

libname sasfiles 'D:\sdtm\data_sas';

%let Root=D:\sdtm\data_xpt;
%xpt2loc(libref=sasfiles, memlist=ae, filespec='&root\ae.xpt');
%xpt2loc(libref=sasfiles, memlist=se, filespec='&root\se.xpt');

How to write the correct one? Thanks!