Monday, February 20, 2006

Re: st: non-parametric tests

On 17 Feabh 2006, at 15:45, ottone@unipmn.it wrote:

> Dear all, > we ran an experiment where we asked people how many tasks they > wanted to > carry out under two different contracts. We ran both the Wilcoxon > and the > Sign tests on that data. I think that both tests check whether people > prefer working more under one of the two contracts. Probably, the > Wilcoxon > test takes the magnitude of the difference into account, while the > sign > test does not. Am I right? > If so, what does it mean if the difference between people’s effort in > contract A and in contract B is significant when I run the Wilcoxon > test > but not when I consider the Sign test? In my mind, the opposite > would be > more plausible…What’s the matter with my conclusions? > Thank you very much for your help

The sign test is a pretty hopless test that loses almost all the information in your data, reducing all differences to positive or negative. I'm not sure it's been used in real life in a while. Go with Wilcoxon.

The same applies to the queries in your other two emails.

Ronán Conroy rconroy@rcsi.ie

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