The purpose of the book

Data measured in the form of angles or two-dimensional orientations are to be found almost everywhere throughout Science. They arise commonly in Biology, Geography, Geology, Geophysics, Medicine, Meteorology and Oceanography, and in many other areas. Typical examples include departure directions of birds or animals from points of release, orientations of fracture planes and linear geographical features, directional movement of animals in response to stimuli, wind and ocean current directions, circadian and other biorhythms, times of day of accident occurrences, and so on.

The last 20 years, and more particularly the last 10 years, have seen a vigorous development of statistical methods for analysing such data, with emphasis on problems of data display, correlation, regression, and analysis of data with temporal or spatial structure. In addition, some of the exciting modern developments in general statistical methodology, particularly nonparametric smoothing methods and bootstrap-based methods, have contributed significantly to the data analyst's ability to make progress with problems which have been relatively intractable. The subject has now reached a point of development at which it seems appropriate to provide a unified and up-to-date account of this material for practical use. In this respect, the present book is a companion volume to Statistical Analysis of Spherical Data (Fisher, Lewis & Embleton 1987) which was concerned with three-dimensional unit vectors or orientations, although developments in nonparametric smoothing and bootstrap methods over the last four years have meant that rather more effective use of them has been possible in this book.