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circstat / pycircstat

Toolbox for circular statistics with Python
MIT License
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Skewness of Von mises distribution using two different methods #76

Closed A-ep93 closed 2 years ago

A-ep93 commented 2 years ago

I want to use the circ_skewness code. Based on the code, there are two methods for calculating skewness:

Pewsey, Metrika, 2004 Statistical analysis of circular data, Fisher, p. 34

However, it seems the results are very different from each other. For instance, when I test for a Von Mises distribution (which should have a skewness of 0), the first method returns a skewness of zero while the second method returns a skewness of the order of thousands. What is causing this problem?

Here is an example of what I mean: I generate a Von Mises distribution with mean 1 and kappa 10 with size 1000: b=circ_vmrnd(1, 10, 1000); I try to find its skewness:

[b b0]=circ_skewness(b) Based on the code , b is the skewnss using Pewsey method and b0 is the skewness using Fisher method. These are the results: b=0

b0= -65.78

Why do we have this difference?

philippberens commented 2 years ago

Well, it is two different measures. The field is much less standardized, so not sure why you find this a problem.