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RE: st: RE: McNemar's test with clustering (Somers D comparisons)


From   "Feiveson, Alan H. (JSC-SK311)" <alan.h.feiveson@nasa.gov>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   RE: st: RE: McNemar's test with clustering (Somers D comparisons)
Date   Mon, 26 Apr 2010 13:12:07 -0500

Roger - 

So in your proposed -somersd- analysis, would you use within, between or vonmises comparisons? With a continuous outcome, I would think that if you want to "remove" the twin effect, the comparisons should be within-cluster. However with a dichotomous predictor and outcome, there might be too many pairs with both responses the same, giving essentially no information. So in view of this would the vonmises comparisons with clustered standard errors be the best way? Or perhaps just  between-cluster comparisons?

Al Feiveson



-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Roger Newson
Sent: Monday, April 26, 2010 12:52 PM
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: RE: McNemar's test with clustering

Yes, you could treat twin pairs as a block. However, as we are sampling 
twin pairs from a population of twin pairs, I would still cluster by 
twin pair, whether I was using -clogit- or -somersd-.

The -somersd- method has the advantage that it outputs a difference 
between proportions. I think more people understand those than 
understand odds ratios, although odds ratios are useful for estimating 
relative risks in a case-control study.

Best wishes

Roger


Roger B Newson BSc MSc DPhil
Lecturer in Medical Statistics
Respiratory Epidemiology and Public Health Group
National Heart and Lung Institute
Imperial College London
Royal Brompton Campus
Room 33, Emmanuel Kaye Building
1B Manresa Road
London SW3 6LR
UNITED KINGDOM
Tel: +44 (0)20 7352 8121 ext 3381
Fax: +44 (0)20 7351 8322
Email: r.newson@imperial.ac.uk
Web page: http://www.imperial.ac.uk/nhli/r.newson/
Departmental Web page:
http://www1.imperial.ac.uk/medicine/about/divisions/nhli/respiration/popgenetics/reph/

Opinions expressed are those of the author, not of the institution.

On 26/04/2010 18:36, Lachenbruch, Peter wrote:
> Could you treat the members of the twin pairs as a block in a randomized block fashion?  The clogit idea sounds pretty good
>
> Tony
>
> Peter A. Lachenbruch
> Department of Public Health
> Oregon State University
> Corvallis, OR 97330
> Phone: 541-737-3832
> FAX: 541-737-4001
>
>
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Laura Gibbons
> Sent: Monday, April 26, 2010 10:10 AM
> To: 'statalist@hsphsun2.harvard.edu'
> Subject: Re: st: RE: McNemar's test with clustering
>
> Sorry this wasn't clear.  For this analysis, I'm just interested in the
> men as individuals, are their right and left sides different.  If I had a
> continous outcome (and no twinship to consider), I'd use a paired t-test.
>
> But the sample happens to be (for other reasons) twins, so I need to
> adjust errors (p-values) for the correlation between twins.
>
> Pair	Twin	Left 	Right
> -----------------------------
> 1	1	1	0
> 1	2	1	1
> 2	1	0	0
> 2	2	1	0
>
> something like that, where I wan't to compare Left and Right, and Pair is
> a nuisance variable to me.
>
> thank you!  Laura
>
>
> On Mon, 26 Apr 2010, Lachenbruch, Peter wrote:
>
>> I seem to be missing something here.  If you take the within-pair
>> difference aren't you removing the pair effect? You can make the same
>> argument for a dichotomous response. In this case the difference will be
>> -1, 0, or 1.  You could do a t-test on this (variance would be slightly
>> off) or you could look at the table of responses and test if the
>> proportion of -1s is the same as the proportion of +1s.  May need to do
>> this by hand, but should be simple. What is the clustering variable if
>> not pairs?
>>
>> Tony
>>
>> Peter A. Lachenbruch
>> Department of Public Health
>> Oregon State University
>> Corvallis, OR 97330
>> Phone: 541-737-3832
>> FAX: 541-737-4001
>>
>>
>> -----Original Message-----
>> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Laura Gibbons
>> Sent: Sunday, April 25, 2010 6:39 PM
>> To: statalist@hsphsun2.harvard.edu
>> Subject: st: McNemar's test with clustering
>>
>> I'd like to do something like McNemar's test, -mcc-, where I'm comparing
>> presence of two dichotomous traits in each person.  [In this case, is a
>> finding more common on the left side of the spine, compared to the right.]
>>
>> The problem is that the subjects are twins, in this analysis a nuisance
>> parameter, but svyset or cluster(pair) are not options for mcc.
>>
>> For continuous outcomes I can get the equivalent of a paired t-test by
>> computing the difference and then getting the p-values from the intercept
>> in
>>
>> reg difference, cluster(pair)
>>
>> but I've not come up with anything along these lines either.
>>
>> Any guidance would be appreciated, thanks!
>>
>> -Laura
>>
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> Laura E. Gibbons, PhD
>> General Internal Medicine, University of Washington
>> Box 359780, Harborview Medical Center, 325 Ninth Ave, Seattle, WA 98104
>> phone: 206-744-1842, fax: 206-744-9917, Office address: 401 Broadway, Suite 5122
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> *
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>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Laura E. Gibbons, PhD
> General Internal Medicine, University of Washington
> Box 359780, Harborview Medical Center, 325 Ninth Ave, Seattle, WA 98104
> phone: 206-744-1842, fax: 206-744-9917, Office address: 401 Broadway, Suite 5122
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> *
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