[R] Chi-square test for trend - where is prop.trend.test?
Peter Dalgaard BSA
p.dalgaard at biostat.ku.dk
Tue Sep 26 10:49:14 CEST 2000
Mark Myatt <mark at myatt.demon.co.uk> writes:
> Peter,
>
> I wrote:
>
> >> Is there a function to do a chi-square test for trend or equivalent in
> >> R. I can write one myself but I was wondering, before I get down to it,
> >> if I need to re-invent the wheel.
>
> You replied:
>
> >Will prop.trend.test do what you want?
>
> The name sounds right. Where do I find this function? I am running RWin
> 1.1.0.
That'll be 0.0.1 too little. It slipped throught the cracks for 1.1.0
and got inserted in 1.1.1
However, it is hardly rocket science:
prop.trend.test <-
function (x, n, score = 1:length(x))
{
method <- "Chi Square Test for Trend in Proportions"
dname <- paste(deparse(substitute(x)), "out of", deparse(substitute(n)))
dname <- paste(dname, ",\n using scores:", paste(score, collapse = " "))
freq <- x/n
p <- sum(x)/sum(n)
w <- n/p/(1 - p)
a <- anova(lm(freq ~ score, weight = w))
chisq <- a["score", "Sum Sq"]
names(chisq) <- "X-squared"
df <- 1
names(df) <- "df"
pval <- 1 - pchisq(chisq, 1)
rval <- list(statistic = chisq, parameter = df, p.value = pval,
method = method, data.name = dname)
class(rval) <- "htest"
return(rval)
}
--
O__ ---- Peter Dalgaard Blegdamsvej 3
c/ /'_ --- Dept. of Biostatistics 2200 Cph. N
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk) FAX: (+45) 35327907
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