[R] replicating the odds ratio from a published study
p.dalgaard at biostat.ku.dk
Fri Jan 26 23:01:11 CET 2007
Bob Green wrote:
> Peetr & Michael,
> I now see my description may have confused the issue. I do want to compare
> odds ratios across studies - in the sense that I want to create a table
> with the respective odds ratio for each study. I do not need to
> statistically test two sets of odds ratios.
> What I want to do is ensure the method I use to compute an odds ratio is
> accurate and intended to check my method against published sources.
> The paper I selected by Schanda et al (2004). Homicide and major mental
> disorders. Acta Psychiatr Scand, 11:98-107 reports a total sample of 1087.
> Odds ratios are reported separately for men and women. There were 961 men
> all of whom were convicted of homicide. Of these 961 men, 41 were diagnosed
> with schizophrenia. The unadjusted odds ratio is for this group of 41 is
> cited as 6.52 (4.70-9.00). They also report the general population aged
> over 15 with schizophrenia =20,109 and the total population =2,957,239.
> Any further clarification is much appreciated,
A fisher.test on the following matrix seems about right:
[1,] 41 20068
[2,] 920 2936210
Fisher's Exact Test for Count Data
data: matrix(c(41, 920, 20109 - 41, 2957239 - 20109 - 920), 2)
p-value < 2.2e-16
alternative hypothesis: true odds ratio is not equal to 1
95 percent confidence interval:
The c.i. is not precisely the same as your source. This could be down to
a different approximation (R's is based on the noncentral hypergeometric
distribution), but the classical asymptotic formula gives
 4.767384 8.918216
which is closer, but still a bit narrower.
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