topic Re: How to analyze cross-over effect in SAS? in Statistical Procedures

How to analyze cross-over effect in SAS?

sy2426 — Thu, 04 Nov 2021 22:23:41 GMT

Hi,

I want to see if there is a carry-over effect in my study and I don't know how do I do so in SAS. Basically, I have three timepoints (baseline, time1, time2). All subject received diet A from baseline to time1, and then they all received diet B from time1 to time2. The study outcome is energy expenditure. There was no washout period in between. I wonder how may I analyze the data to investigate if energy expenditure from time1 to time2 is affected/carried over by diet A? Attached is my sample data. TEE_change is the outcome. Period=ru is from baseline to time1, Period=TD is from time1 to time2. I want to see if tee_change during period=TD is affected by diet=VLC. Thank you so much in advance!

Thanks,

Re: How to analyze cross-over effect in SAS?

sbxkoenk — Thu, 04 Nov 2021 23:08:34 GMT

Hello,

Paper PO16
Estimate Carryover Effect in Clinical Trial Crossover Designs
David Shen, WCI, Inc.
Zaizai Lu, AstraZeneca Pharmaceuticals
https://www.lexjansen.com/pharmasug/2006/Posters/PO16.pdf

Paper 221
CROSS CROSSOVER STUDIES OFF YOUR LIST
Pippa M. Simpson, University of Arkansas for Medical Sciences, Little Rock, Arkansas
Robert M. Hamer, UMDNJ Robert Wood Johnson Medical School, Piscataway, NJ
Shelly Lensing, University of Arkansas for Medical Sciences, Little Rock, Arkansas
https://support.sas.com/resources/papers/proceedings/proceedings/sugi24/Posters/p221-24.pdf

Good luck,

Koen

Re: How to analyze cross-over effect in SAS?

sy2426 — Thu, 04 Nov 2021 23:42:34 GMT

Hi Koen,

Thank you so much! The article "Estimate Carryover Effect in Clinical Trial Crossover Designs" is super helpful. However, in my case, there is no "sequence" variable, because everyone have one diet during period A, and other diet during period B. So I have no "sequence" variable to add to the t-test.

Thanks,

Shui

Re: How to analyze cross-over effect in SAS?

ballardw — Thu, 04 Nov 2021 23:47:03 GMT

@sy2426 wrote:

Hi Koen,

Thank you so much! The article "Estimate Carryover Effect in Clinical Trial Crossover Designs" is super helpful. However, in my case, there is no "sequence" variable, because everyone have one diet during period A, and other diet during period B. So I have no "sequence" variable to add to the t-test.

Thanks,

Shui

Period A is sequence 1, Period B is sequence 2 most likely if B was done after A. Or if all of your subjects have the same diet for period A and the same different at Period B you may be looking for a Paired T-test

Re: How to analyze cross-over effect in SAS?

Ksharp — Fri, 05 Nov 2021 12:21:09 GMT

It is repeated measure test . I think should try Mixed model.

or calling @StatDave @SteveDenham @lvm

Re: How to analyze cross-over effect in SAS?

SteveDenham — Fri, 05 Nov 2021 13:53:04 GMT

I really don't see a good way to estimate any carry-over effect. A repeated measures analysis or a paired t test (simplest case of repeated measures) can let you know if there is a difference between treatments, but without either a "blank" period following Treatment A or a true AB/BA crossover, carryover is not estimable.

SteveDenham

Re: How to analyze cross-over effect in SAS?

sy2426 — Fri, 05 Nov 2021 15:02:41 GMT

Thanks Ksharp!

Re: How to analyze cross-over effect in SAS?

sy2426 — Fri, 05 Nov 2021 15:04:34 GMT

Thank you SteveDenham, that makes sense. I don't see how mixed effect model and paired t-test can help to estimate carry-over effect neither.

Re: How to analyze cross-over effect in SAS?

Ksharp — Sat, 06 Nov 2021 09:57:21 GMT

If it was frequency data , PROC FREQ 's Trend Analysis is very like this, but no paired .
Or could you run Covariance Analysis if you have 'before' and 'after' data .

maybe @Rick_SAS know something .

Re: How to analyze cross-over effect in SAS?

sy2426 — Mon, 08 Nov 2021 14:53:03 GMT

Thanks Ksharp. I contacted SAS support and got the same answer- carryover effect cannot be estimated for my data structure.

Re: How to analyze cross-over effect in SAS?

Ksharp — Tue, 09 Nov 2021 12:00:03 GMT

Yeah. Glad you get answer. Today I go through PROC TTEST documentation.

And find this interesting thing, but still not paired .