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help for circcorr
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Correlation for circular data

        circcorr varname1 varname2 [if exp] [in range]


Description 

    circcorr produces a correlation coefficient appropriate for two circular
    variables taking on values between 0 and 360 degrees.  The correlation is
    defined for n values of two such variables x and y as

                       SUM sin(x[i] - x[j]) sin(y[i] - y[j])
                       i<j
        r_T =   ----------------------------------------------------
                              2                     2
                ROOT [ SUM sin (x[i] - x[j]) SUM sin (y[i] - y[j]) ]
                       i<j                   i<j

    and takes on values between -1 and 1.

    The P-value associated with r_T can be computed for large samples, say n
    >= 25, but depends on the distribution of x and y.  If either has a mean
    resultant length (vector strength) of 0, then n * r_T is double
    exponential. Otherwise, ROOT of n * r_T has a Gaussian (normal)
    distribution. Both P-values are calculated.  See Fisher (1993,
    pp.151-153) for details, but note that both U terms in (6.40) on p.152
    should be rooted.


Example 

    . circcorr wallasp axisasp


Reference

    Fisher, N.I. 1993. Statistical analysis of circular data.  Cambridge:
        Cambridge University Press.


Author 

    Nicholas J. Cox, University of Durham, U.K.
    n.j.cox@durham.ac.uk


Also see 

On-line: help for circscatter, circlccorr