Testing for departure from uniformity and estimating mean direction for circular data. 2017

Graeme D Ruxton
School of Biology, University of St Andrews, St Andrews KY16 9TH, UK graeme.ruxton@st-andrews.ac.uk.

Although circular data are common in biological studies, the analysis of such data is often more rudimentary than it need be. One of the most common hypotheses tested is whether the data suggest that samples are clustered around a certain specified direction, rather than being uniformly spread across all possible directions. Here, I use data from a recent publication on the compass directions of epiphytes and mistletoes on tree trunks. This is used to demonstrate how with relatively little extra work researchers can improve the rigour of testing such hypotheses, and this improved rigour can lead to biological insights missed by simpler analyses. Specifically, I highlight that a much broader range of null hypotheses can be tested than current practice, and that a range of methods are available for estimating a confidence interval for mean direction. I offer advice on appropriate selection for both tests and parameter estimation methods, and highlight the need to correct for the fact that sample estimates are biased estimates of population parameters for circular data.

UI MeSH Term Description Entries
D014784 Mistletoe Parasitic plants that form a bushy growth on branches of host trees which are in the order Santalales. It includes the Christmas mistletoe family (VISCACEAE), the showy mistletoe family (LORANTHACEAE) and the catkin mistletoe family (Eremolepidaceae). The composition of toxins, lectins, tyramine, phenethylamines, and other compounds may be affected by the host. Mistletoes

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