[R] Mann-Whitney & Wilcoxon Rank Sum
Peter Dalgaard
p.dalgaard at biostat.ku.dk
Mon May 16 08:34:27 CEST 2005
Prof Brian Ripley <ripley at stats.ox.ac.uk> writes:
> as essentially
>
> r <- rank(c(x,y))
> sum(r[seq(along = x)]) - n.x * (n.x + 1)/2
>
> I guess your reference just uses the first term.
>
> Another way of looking at this is whether ranks start at 0 or at 1 (as
> in rank()): R's definition is the rank sum with 0-based ranks.
Er, no... Then you'd be subtracting n.x. The definition is such that
the minimum value of the statistic becomes zero (2nd term is equal to
sum(1:n.x)).
--
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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