[R] p value of trends for odds ratios (or hazard ratios)

Michael Friendly friendly at yorku.ca
Sun Jan 5 16:09:34 CET 2014

On 1/4/2014 12:39 AM, zhu yao wrote:
> Dear Sir
> Many papers calculated the p value of trends for odds ratios of ordered
> category variables. I have found the tabodds command in Stata. But how to
> do it in R?
> Thanks
> *Yao Zhu*

If what you are looking at is a 2 x 2 x k table, where you want the odds
ratios for the k strata, which are ordered, perhaps something like this:

data("CoalMiners", package="vcd")

## Log Odds Ratio Plot
lodds <- oddsratio(CoalMiners)

plot(lodds, lwd=2, cex=1.25, pch=16,
      xlab = "Age Group",
      main = "Breathlessness and Wheeze in Coal Miners")

age <- seq(25, 60, by = 5)
mod <- lm(lodds ~ poly(age,2))
lines(fitted(mod), col = "red", lwd=2)

Tests of the coefficients in mod give the tests of linear and quadratic
changes in the odds ratio with age.

Michael Friendly     Email: friendly AT yorku DOT ca
Professor, Psychology Dept. & Chair, Quantitative Methods
York University      Voice: 416 736-2100 x66249 Fax: 416 736-5814
4700 Keele Street    Web:   http://www.datavis.ca
Toronto, ONT  M3J 1P3 CANADA

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