topic PROC MIXED with nested/clustered repeated measures in Statistical Procedures

PROC MIXED with nested/clustered repeated measures

tka726 — Tue, 08 Feb 2022 03:11:51 GMT

Hello -

I’m running a repeated measures mixed model with lab data. For each patient - lab value is measured at 4 timepoints, but at each timepoint the lab data value is measured by 2 separate devices. Each patient was also randomized to one of 2 treatments. I am interested in testing the difference in lab values by treatment, timepoint, and device.

Each patient has results at 4 timepoints, for 2 devices (8 records per patient). I am unsure how to specify the nested/clustered nature of device and patient. In the repeated statement, I included subject = ptno(device) - is this correct?

Thanks!!

PROC MIXED DATA=labdat;

CLASS ptno device time trt;

MODEL labval = device time trt device*time trt*device trt*time trt*device*time;

REPEATED time / subject=ptno(device) type=cs;

LSMeans device*time*trt/ cl DIFF;

run;

Each patient has 8 records (2 devices, 4 timepoints each):

ptno trt device time labval

1 1 1 1 99

1 1 1 2 105

1 1 1 3 520

1 1 1 4 467

1 1 2 1 267

1 1 2 2 325

1 1 2 3 261

1 1 2 4 313

....

20 2 1 1 119

20 2 1 2 127

20 2 1 3 618

20 2 1 4 529

20 2 2 1 267

20 2 2 2 320

20 2 2 3 290

20 2 2 4 400

@SteveDenham, any suggestions?

Re: PROC MIXED with nested/clustered repeated measures

SteveDenham — Tue, 08 Feb 2022 14:48:42 GMT

This looks as though it should work. Is there something in the log or listing that indicates that there is an issue?

SteveDenham

Re: PROC MIXED with nested/clustered repeated measures

jiltao — Tue, 08 Feb 2022 14:50:34 GMT

There are different ways to model the correlations in this data. One approach is to use the kronecker product covariance structure --

repeated device time / subject=patno type=un@ar(1); *** or un@un or un@cs;

Other ways are also possible, including using both RANDOM and REPEATED statements. See my paper below (pages 4 and 5 are relevant here).

https://support.sas.com/resources/papers/proceedings15/SAS1919-2015.pdf

Hope this helps,

Jill

Re: PROC MIXED with nested/clustered repeated measures

SteveDenham — Tue, 08 Feb 2022 14:52:52 GMT

Follow @jiltao 's advice. She is who I would turn to if I had any questions.

SteveDenham

Re: PROC MIXED with nested/clustered repeated measures

tka726 — Tue, 08 Feb 2022 17:01:48 GMT

Thank you, both.

This paper perfectly answers my questions!