Clustering in space
Choose one: the hypothesized clustering is
- global - Is there clustering anywhere?
- local - Is there clustering here (in a
local area)?
- focused - Is there clustering around a
focus of suspected hazard?
Want more help? Here's Dr. Art
Getis describing these tests:
- Global Cluster test:
A test that attempts to answer the question: Within the study area
are there one or more statistically significant spatial clusters of the
georeferenced variable of interest? (the actual locations of the clusters
are not implied) Or, is there a spatial pattern that could not have
arisen by chance? (this implies a test for clustering or dispersion
or both).
- Local Cluster test:
Within the study area can one consider particular georeferenced
observations to be members of statistically significant spatial clusters?
(location is implied) Or, are the neighbors of i to some distance d
closer together (or have a greater/lesser magnitude) than chance would
have it?
- Focused Cluster test:
A variation on the latter, i.e., within the study area can one
identify a particular location (point or place) to be a member of
a statistically significant cluster? (location is implied)
The distinction between the last two is a function of the hypothesis
being tested. Local implies a search for clusters, focused does not.
In the end, more than one focused test gives rise to local
tests. Nothing has been said about the independence of tests, however.
Website maintained by Andy
Long. Comments appreciated.
longa@nku.edu