Re: Replacement of clusters by individuals

[Steve Buckland]

Johanna, the methods are very robust to failures of the independence
assumption, which means that, in your case, you would be better to
analyse the data ignoring clusters. If there are 6 animals in a group,
record 6 individual distances. This can cause the goodness-of-fit test
statistics to give spurious significant results, but otherwise causes
few problems. You can also record which animals were part of the same
herd, which allows you to analyse the data either way for example, to
assess whether it makes any practical difference. You then need to find
a mean distance from the line of a group - for a group that has
individuals both sides of the line, you need to be careful to record
distances on one side as negative, before taking the mean distance.

Steve Buckland

BRinK wrote:
> > Dear all,
> >
> > Is there a way to deal with animals that form loose aggregations rather than
> > defined groups (clusters). The data that was collected was in the form of
> > clusters, where most individuals were detected as single objects, but once
> > in while two to six. Antelopes such as Springbok in Southern Africa do form
> > herds, but when food is abundant, the herds can spread over miles, which
> > makes it difficult to define a herd. Then again, occasionally they do form
> > i.e. bachelor herds.
> > Can the data collected as clusters be replaced by individuals. Does this
> > greatly violate the assumptions of distance? When data is collected, should
> > all animals be collected as single objects, even though they do sometimes
> > occur in smaller groups (violation of independence)? It might also be that
> > the Springbok is a difficult case. Would another option be to do an analysis
> > seperately for clusters and non-clusters and then add the estimates to
> > obtain a global estimate?
> >
> > thanks for any suggestions on the topic: loose aggregations.
> >
> > Johanna.
> >
> >
> > ***************************************************
> > BRinK - Biological Research in Kuzikus
> >
> > Email: brinkn...@gmail.com
> > Web: http://brinknamibia.googlepages.com
> > ***************************************************
> >
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____________________________________________________________________

Stephen T. Buckland

CREEM, The Observatory, Buchanan Gdns, St Andrews KY16 9LZ, Scotland

Tel. +44 (0)1334 461841 Secretary +44 (0)1334 461842

Fax +44 (0)1334 461800 e-mail st...@mcs.st-and.ac.uk
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Professor of Statistics http://www.mcs.st-and.ac.uk/

Director, NCSE http://www.ncse.org.uk/

Director, CREEM http://www.creem.st-and.ac.uk/



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[BRinK]