Association indices were originally developed to describe species co-occurrences,
but have been used increasingly to measure associations between individuals.
However, no statistical method has been published which allow testing the
extent to which the observed association index values differ from those
of a randomly associating population. Here, we describe an adaptation of
a test developed by Manly (1995), which uses the observed association data
as a basis for a computer-generated randomisation. The observed pattern
of association is tested against a randomly created one while retaining
important features of the original data, e.g., group size and sighting
frequency. We applied this new method to test four data sets of associations
from two different Hector's dolphin populations. The test demonstrated
that populations with similar median Half Weight Index values showed clear
differences in association patterns, i.e. some were associating non-randomly
whereas others showed no evidence thereof. Hence, we argue that the magnitude
of an index value is not useful to describe the strength of an association
unless tested against a randomised data set.