MATLAB functions to analyze directional (azimuthal) data—II: Correlation

Data that represent azimuthal directions cannot be analyzed in the same manner as ordinary linear variables that measure, for example, size or quality. This is especially true for correlations between variables. Although many statistical techniques have been developed for dealing with directional data, software is scarce for the unique calculations. This paper describes a MATLAB script, located on the IAMG server, that calculates measures of association (correlations) between two circular variables, or between a circular and a linear variable. The calculations include tests of significance of the associations. These tests use large-sample approximations or resampling methods.