karel.zvara@mff.cuni.cz writes:
> Full_Name: Karel Zvara
> Version: 1.8.1
> OS: MS Winows 2000
> Submission from: (NULL) (195.113.30.163)
>
>
> The test statistics of the fligner.test (ctest package) depends on the
order of
> cases:
>
> > fligner.test(count~spray,data=InsectSprays)
>
> Fligner-Killeen test for homogeneity of variances
>
> data: count by spray
> Fligner-Killeen:med chi-squared = 14.4828, df = 5, p-value > 0.01282
>
> >
fligner.test(count~spray,data=InsectSprays[order(InsectSprays$count),])
>
> Fligner-Killeen test for homogeneity of variances
>
> data: count by spray
> Fligner-Killeen:med chi-squared = 5.4527, df = 5, p-value > 0.3632
>
> > fligner.test(count~spray,data=InsectSprays[order(sample(72)),])
>
> Fligner-Killeen test for homogeneity of variances
>
> data: count by spray
> Fligner-Killeen:med chi-squared = 2.7349, df = 5, p-value > 0.7408
>
> The problem lies, I think, in the ordering of centered values x:
>
> x <- unlist(tapply(x, g, function(u) u - median(u)))
Right. x is not in the same order as g is after that operation, so
the two lines that come immediately after are incoherent:
a <- qnorm((1 + rank(abs(x))/(n + 1))/2)
STATISTIC <- sum(tapply(a, g, "sum")^2/tapply(a, g,
"length"))
I think the unlist construction wants to be replaced with
x <- x - tapply(x,g,median)[g]
--
O__ ---- Peter Dalgaard Blegdamsvej 3
c/ /'_ --- Dept. of Biostatistics 2200 Cph. N
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk) FAX: (+45) 35327907