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Re: st: RE: Signtest (statistics question), thanks and a further question
At 16:04 12/05/03 +0000, Guillaume Frechett wrote:
Thanks to the three guys that responded. Nick Cox wrote:
My understanding (which I think is confirmed by Roger Newson's answer --
see below) was that since I have paired observations Ranksum would be
-ranksum- works quite well in this situation.
Roger, should I understand from your answer that there are tests taking
into consideration what I am talking about but that 1) I have to read your
thesis to learn about it, and 2) that it wouldn't be trivial to code? We
can move this discussion to direct email if that is more appropriate.
In the paired case, you do not have to read my thesis to learn about the
test to use. You simply type
and you get a CI for the unconditional mean signed difference
(corresponding to Kendall's tau-a). If you then type
ci sgndif if sgndif!=0
then you get a CI for the conditional mean signed difference (corresponding
to Somers' D). My thesis extended the principle to groups larger than
pairs, eg extended families of yeast cells or mouse embryo cells.
I can send Guillaume a pre-publication draft of my Stata Journal insert if
he wants. It includes an example of using -ranksum- and -somersd- to
compare 2 independent groups, ie American cars and non-American cars. As
Guillaume says, -ranksum- is not appropriate in the paired case.
Lecturer in Medical Statistics
Department of Public Health Sciences
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