Help using Base SAS procedures

"proc mixed repeated" - Is this right !?

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"proc mixed repeated" - Is this right !?

Based on the limited information I have provided, Mr. D (a dedicated contributor at this forum) has kindly provided me a base code for my ‘drug test’ scenario. I trust his base code, while I am not certain of the modifications I have made to it. Please take a look and see if the code below looks alright. Thanks in advance.

Scenario:
A specific drug X is administered to patients at various dosages (DOSE), and the change in patients’ heart rates is monitored hourly (PATIENT, HEARTRATE, and TIME). Men and women are tested separately (GENDER). Also, prior to assigning patients to a certain dosage, three weight categories (BLOCK) are created.


proc mixed data=mydata;
class dose patient time gender block;
model heartrate= dose|time|gender;
random block;
repeated time /subject=patient(dose*gender*block) type=un;
run;


Any suggestions/comments are greatly appreciated. Especially, I am not sure how to handle the block effect in the proc mixed repeated procedure.
Respected Advisor
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Re: "proc mixed repeated" - Is this right !?

The statements you have will give marginal means averaging over blocks. This seems logical to me, as the realization of blocks in this particular study is a sample from all possible blocks.

I think your measurements are at equal intervals, and if there are more than three or four, you may wish to use a time-dependent covariate structure, rather than the unstructured matrix, simply because the number of parameters to be estimated is smaller. You could check the AIC for this.

Finally, you may want BLUPs for heartrate for the three blocks. These differe from the marginal means (lsmeans), but can be obtained from estimate statements. See the documentation for examples.

Good luck.

Steve Denham
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Re: "proc mixed repeated" - Is this right !?

Thanks a lot Steve!
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Re: "proc mixed repeated" - Is this right !?

Hi again. I am trying to modify the above ‘drug test’ scenario to accommodate “unequal” measurement intervals. Using the SAS book as a reference, I made the following modifications:

- Base line heartrate measurement at T=0 is made into a separate entry as BASEHEARTRATE
- New entry TIME1 is created which is identical to TIME to be used in the REPEATED statement
- Chanes indicated in the upper letters

proc mixed data=mydata ORDER=DATA;
class dose patient time gender block;
model heartrate= dose|time|gender BASEHEARTRATE;
random block;
repeated time /subject=patient(dose*gender*block) type= SP(POW)(TIME1);
run;

This seems to run o.k., but is this right? Also, I don’t understand:
- why you need ORDER=DATA?
- why you need BASEHEARTRATE for “unequal” intervals but not for the “equal” intervals?
(==> Without BASEHEARTRATE in the MODEL statement, does it not account for the pre-treatment differences (i.e., differences in the individual heartrate at T=0?))
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Re: "proc mixed repeated" - Is this right !?

Correction: - Changes are indicated in uppercase letters.
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