hi,
when performing a wilcox.test or a wilcox.exact i get results that looks
like this:
wilcox.exact(x, mu=.5)
Exact Wilcoxon signed rank test
data: x
V = 207, p-value = 0.0006905
alternative hypothesis: true mu is not equal to 0.5
the way i understand the wilcox.test (or wilcox.exact) the V-value
represents the summed up ranks of either the positive or negative
differences, whichever sum is BIGGER.
to actually look up the p-value in a table (and to quote it in a
publication) i need the T value, which to my understanding is the summed
up ranks of either the positive or negative differences, whichever sum
is SMALLER.
so i guess my question is: how do i get the T-value
thanks,
jan
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V-value in the wilcox.test resp. wilcox.exact
3 messages · Jan M. Wiener, Peter Dalgaard, Torsten Hothorn
Jan Malte Wiener <jan.wiener at tuebingen.mpg.de> writes:
the way i understand the wilcox.test (or wilcox.exact) the V-value represents the summed up ranks of either the positive or negative differences, whichever sum is BIGGER. to actually look up the p-value in a table (and to quote it in a publication) i need the T value, which to my understanding is the summed up ranks of either the positive or negative differences, whichever sum is SMALLER. so i guess my question is: how do i get the T-value
At least for wilcox.test, V is the sum of the *positive* ranks. The sum of the negative ranks can be obtained by switching the sign on x and mu. In the absence of ties and exact zeros, the two rank sums add up to sum(1:N) == N*(N+1)/2 If ties are present, standard tables are wrong anyway...
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 -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
hi,
when performing a wilcox.test or a wilcox.exact i get results that looks
like this:
wilcox.exact(x, mu=.5)
Exact Wilcoxon signed rank test
data: x
V = 207, p-value = 0.0006905
alternative hypothesis: true mu is not equal to 0.5
the way i understand the wilcox.test (or wilcox.exact) the V-value
represents the summed up ranks of either the positive or negative
differences, whichever sum is BIGGER.
no. wilcox.test computes the statistic along the following lines
x <- x - mu
ZEROES <- any(x == 0)
if(ZEROES)
x <- x[x != 0]
...
r <- rank(abs(x))
STATISTIC <- sum(r[x > 0])
i.e. the sum of the ranks of the absolute values of x which belong
to positive values of x.
to actually look up the p-value in a table (and to quote it in a publication) i need the T value, which to my understanding is the summed up ranks of either the positive or negative differences, whichever sum is SMALLER.
wilcox.test computes the p-value for you, no need to look up tables. Torsten
so i guess my question is: how do i get the T-value thanks, jan -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
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