[R] Conditional logistic regression on n:m matched "cohort" data

Robert A. LaBudde ral at lcfltd.com
Mon Jul 23 04:33:54 CEST 2007

I am designing an interlaboratory validation study for a 
presence/absence alternative method test kit vs. a presence/absence 
reference method test kit.

There will be 10 laboratories conducting tests using both methods. In 
each laboratory, there will be 5 specimens tested, each of the 5 
specimens twice by both methods (alternative, standard).

The total number of data are 10 x 5 x 4 = 200.

The general structure is as follows:

id: sequential result label, 1 to 200.
lab: a factor which has 10 levels, one for each participating lab.
specimen: 1 to 5 in each lab, no connection between labs.
method: A or R.
result: 0 or 1 (absence or presence).

This experiment appears to be equivalent to a matched cohort study. 
The matching is done on specimens, and there are 2 alternative and 2 
reference results for each specimen.

The sketchy description for clogit() of package "survival" presumes a 
matched case-control study is being analyzed.

I am looking for the correct syntax to use in clogit() for this experiment.


clogit(result ~ lab + strata(specimen), method="exact", data=mydata)

all that is required?

Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: ral at lcfltd.com
Least Cost Formulations, Ltd.            URL: http://lcfltd.com/
824 Timberlake Drive                     Tel: 757-467-0954
Virginia Beach, VA 23464-3239            Fax: 757-467-2947

"Vere scire est per causas scire"

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