Hi Wei,
Based on my understanding, you are facing issues in getting the z-value in MATLAB for some cases. To resolve this issue, you can refer the following steps:
The ‘zval’ is not generated in the first case as the values are all identical. Hence, this is a degenerate case of all ties.
Now to generate the ‘zval’ in such cases , we can create a default value for ‘zval’ and generate it like this:
[p1,h1,stats1] = signrank(Pair1_A,Pair1_B,'tail','both','alpha',0.05,'method','approximate') ;
if ~isfield(stats1, 'zval')
stats1.zval = nan;
end
[p,h,statsrnd1] = signrank(Pair1_A,Pair1_B+randn(size(Pair1_B)));
statsvector1 = [stats1;statsrnd1]
Additionally, the type of the hypothesis result being returned as double instead of logical is also due to the values being treated as ties.
‘signrank’ function uses a tolerance defined as ‘epsdiff = eps(x) + eps(y)’. It calculates the absolute differences and considers values with ‘abs(d(i)) < epsdiff’ as ties.
To know more about this, you can refer to the following documentation link:
Hope this answers your query!
