Re: [R] value of W seems to be suspicious in the mann-whitney wilcox related test. what could be the problem

From: Abhijit Dasgupta <aikidasgupta_at_gmail.com>
Date: Mon, 14 Mar 2011 11:16:21 -0400

You need to read up on the Wilcoxon signed-rank test and the output from wilcox.test!!!

The confidence interval is of the difference of medians, which can certainly be negative. In fact, your estimate is -33, and the confidence interval is (-68, 0) which is reasonable.

The value of W is a positive number, in general, and isn't restricted to [0,1]

Abhijit
>
> On 3/14/2011 11:07 AM, taby gathoni wrote:
>> my output is as follows:
>> wilcox.test(main_samp$SCORE~main_samp$GENDER, conf.int = TRUE)
>>
>> Wilcoxon rank sum test with continuity correction
>>
>> data: main_samp$SCORE by main_samp$GENDER
>> W = 2780.5, p-value = 0.04829
>> alternative hypothesis: true location shift is not equal to 0
>> 95 percent confidence interval:
>> -6.800005e+01 -2.056837e-05
>> sample estimates:
>> difference in location
>> -33.00003
>> result of W seems suspicious since i expect the result to be between 0 and 1.
>>
>> and the confidence intervals are also -ves what could be the challenge?
>> Thanks Taby
>>
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