Comparing the performances of Diggle's tests of spatial randomness for small samples with and without edge-effect correction: Application to ecological data
J. Gignoux et al., Comparing the performances of Diggle's tests of spatial randomness for small samples with and without edge-effect correction: Application to ecological data, BIOMETRICS, 55(1), 1999, pp. 156-164
Diggle's tests of spatial randomness based on empirical distributions of in
terpoint distances can be performed with and without edge-effect correction
. We present here numerical results illustrating that tests without the edg
e-effect correction proposed by Diggle (1979, Biometrics 35, 87-101) have a
higher power for small. sample sizes than those with correction. Ignoring
the correction enables detection of departure from spatial randomness with
smaller samples (down to 10 points vs. 30 points for the tests with correct
ion). These results are confirmed by an example with ecological data consis
ting of maps of two species of trees in a West African savanna. Tree number
s per species per map were often less than 20. For one of the species, for
which maps strongly suggest an aggregated pattern, tests without edge-effec
t correction enabled rejection of the null hypothesis an three plots out of
five vs. on only one for the tests with correction.