Chapter 2: Tests of homogeneity of dispersions (PERMDISP)
Key reference
Method: Anderson (2006)
2.1 General description
Key reference Method: PERMDISP is a routine for testing the homogeneity of multivariate dis...
2.2 Rationale
There are various reasons why one might wish to perform an explicit test of the null hypothesis o...
2.3 Multivariate Levene’s test (Bumpus’ sparrows)
proposed doing an analysis of variance (ANOVA) on the absolute values of deviations of observati...
2.4 Generalisation to dissimilarities
Of course, in many applications that we will encounter (especially in the case of community data)...
2.5 $P$-values by permutation
The other hurdle that must be cleared is to recognise that, in line with the philosophy of all of...
2.6 Test based on medians
Levene’s test (for univariate data) can be made more robust (i.e. less affected by outliers) by u...
2.7 Ecological example (Tikus Island corals)
An ecological example of the test for homogeneity is provided by considering a study by on coral...
2.8 Choice of measure
An extremely important point is that the test of dispersion is going to be critically affected by...
2.9 Dispersion as beta diversity (Norwegian macrofauna)
When used on species composition (presence/absence) data in conjunction with certain resemblance ...
2.10 Small sample sizes
There is one necessary restriction on the use of PERMDISP, which is that the number of replicate ...
2.11 Dispersion in nested designs (Okura macrofauna)
In many situations, the experimental design is not as simple as a one-way analysis among groups. ...
2.12 Dispersion in crossed designs (Cryptic fish)
When two factors are crossed with one another, there may be several possible hypotheses concernin...
2.13 Concluding remarks
PERMDISP is designed to test the null hypothesis of no differences in dispersions among a priori ...