What is a cluster?
GAM is a cluster hunter but what is a cluster? The simplest way of
defining a cluster is as a localised excess incidence rate that is unusual
in that there is more of some variable than might be expected. Examples
would include: a local excess disease rate, a crime hot spot, a
unemployment black spot, unusually high positive residuals from a model,
the distribution of a plant or surging glaciers or earthquake epicentres,
pattern of fraud etc. Virtually any variable that has a geographical
distribution can be input into GAM. The assumption is that identifying
these extreme areas (or outliers or unusual areas) may be useful in that
there could be implicit geographical associations with other variables that
can be identified and would be of interest. Pattern detection via the
identification of clusters is a very simple and generic form of
geographical analysis that has many applications in many different
contexts. The emphasis is on localised clustering or patterning because
this may well contain the most useful information.
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Last modified: Wed Feb 25 15:55:15 GMT 1998