[R] Conditional logistic regression on n:m matched "cohort" data [Corrected]
Robert A. LaBudde
ral at lcfltd.com
Mon Jul 23 04:45:10 CEST 2007
[Corrected the model formula to include "method".]
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 + method + 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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