Why is Matlab signrank function returns the same signed rank statistic values when flipping the signs of the data points?
I have a sequence of data points stored in vector x. I use signrank(x) to do sign rank test.
When you use the test for one sample, then W is the sum of the ranks of positive differences between the observations and the hypothesized median value M0 (which is 0 when you use signrank(x) and m when you use signrank(x,m)).
So I think the result signrank(x) and signrank(-x) should be different. But I have experienced some examples, and I get the same sign rank statistic value for x and -x. How is the signed rank statistic defined in Matlab signrank function?