Baseline study Fish, fry and commercial fishery Nysted Offshore ...

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Figure: 3.10.2. Graphic outline of the procedures in a multivariate distance based test of interaction
between criteria of sectioning. (Legendre and Anderson, 1999).
The other method NPMANOVA (Non-parametric multivariate analysis of variance)
(Anderson, 2001) provides a method based on distance-metric of your own choice and
the product is an analysis of a variance table similar to one from the well-known
analysis of variance. In the variance analytical table, the total sums of squares of
distances are divided into sums of squares belonging to each of the factors of the
analysis such as time, place, and the interaction between them. Again, as in the common
ANOVA, these sums of squares are the basis for the F ratios, which again can be tested
for significance using permutations tests. If the distances are calculated as Bray-Curtis
dissimilarities then they also have to be treated in different ways before they can be
used in the NPMANOVA procedure.
It is important to note that both methods can only be used if certain assumptions are
fulfilled just like the requirements to a parametric ANOVA/MANOVA. In principle, the
requirements are the same except that the data do not have to be normal distributed. The
data should still be independent, the effects in the model (time and place) should be
additive and finally the variation should be uniform between the groups. The
SEAS. Baseline study – Fish, fry and commercial fishery Dok. nr. 2148-03-001-rev3 2P.doc