On Aug 31, 2012, at 7:20 AM, Diana Marcela Martinez Ruiz wrote:
> Hi all,
>
> I want to know how to perform the test Breslow-Day test for homogeneity of
> odds ratios (OR) stratified for svytable. This test is obtained with the
> following code:
>
> epi.2by2 (dat = daty, method = "case.control" conf.level = 0.95,
missing comma here ...........................^
> units = 100, homogeneity = "breslow.day", verbose = TRUE)
>
> where "daty" is the object type table svytable consider it, but when I run
> the code
> does not throw the homogeneity test.
You are asked in the Posting guide to copy all errors and warnings when asking
about unexpected behavior. When I run epi.2y2 on the output of a syvtable
object I get no errors, but I do get warnings which I think are due to
non-integer entries in the weighted table. I also get from a svytable()
usingits first example on the help page an object that is NOT a set of 2 x 2
tables in an array of the structure as expected by epi.2by2(). The fact that
epi.2by2() will report numbers with labels for a 2 x 3 table means that its
error checking is weak.
This is the output of str(dat) from one of the example on epi.2by2's help page:
> str(dat)
table [1:2, 1:2, 1:3] 41 13 6 53 66 37 25 83 23 37 ...
- attr(*, "dimnames")=List of 3
..$ Exposure: chr [1:2] "+" "-"
..$ Disease : chr [1:2] "+" "-"
..$ Strata : chr [1:3] "20-29 yrs" "30-39 yrs" "40+ yrs"
Notice that is is a 2 x 2 x n array. (Caveat:: from here on out I am simply
reading the help pages and using str() to look at the objects created to get an
idea regarding success or failure. I am not an experienced user of either
package.) I doubt that what you got from svytable is a 2 x 2 table. As
another example you can build a 2 x 2 x n table from the built-in dataset:
UCBAdmissions
DF <- as.data.frame(UCBAdmissions)
## Now 'DF' is a data frame with a grid of the factors and the counts
## in variable 'Freq'.
dat2 <- xtabs(Freq ~ Gender + Admit+Dept, DF)
epiR::epi.2by2(dat = dat2, method = "case.control", conf.level = 0.95,
units = 100, homogeneity = "breslow.day", verbose = TRUE)$OR.homog
#-------------
test.statistic df p.value
1 18.82551 5 0.00207139
Using svydesign and svytable I _think_ this is how one would go about
constructing a 2 x 2 table:
tbl2<-svydesign( ~ Gender + Admit+Dept, weights=~Freq, data=DF)
summary(dclus1)
(tbl2by2 <- svytable(~ Gender + Admit+Dept, tbl2))
epiR::epi.2by2(dat = tbl, method = "case.control", conf.level = 0.95,
units = 100, homogeneity = "breslow.day", verbose = TRUE)$OR.homog
#-----------------------
test.statistic df p.value
1 18.82551 5 0.00207139
(At least I got internal consistency. I see you copied Thomas Lumley, which is
a good idea. I'll be happy to get corrected on any point. I'm adding the
maintainer of epiR to the recipients.)
--
David Winsemius, MD
Alameda, CA, USA
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