Hi Barnard,

I have used a difference test of group means for circular data (such as mean coupling angles). As Ross said, it is available in the Batschelet book. I have also used a Watson-Wiliams test prior to the means test to ensure that my data were normally (circularly) distributed - sometimes they were not. I performed the tests by hand (with Matlab), and did not use any software suites.

Good luck,
Ryan