GEOSTATS: SUM: spatial t-test
- Original Question:
> Is there a spatial equivalent to the non-spatial t-test? I've got twoReplies:
> samples that I want to compare, but one is auto-correlated. I produced
> the auto-correlated sample using kriging, so I don't want to take out the
> spatial info.
From Carlos Carroll <carlos@...>
> THe CRH modified t-test may be useful. See Clifford et al. 1989.SOME EXCELLENT REFERENCES! CLIFFORD'S ARTICLE, "ASSESSING THE
> Biometrics 45:123-134, or for an application , see Thomson et al. 1996.
> Ecology 77:1698-1715.
SIGNIFICANCE OF THE CORRELATION BETWEEN TWO SPATIAL PROCESSES" IS A GREAT
ANOTHER GOOD REFERENCE (IN FACT, A RESPONSE TO CLIFFORD'S ARTICLE) IS:
DUTILLEUL, PIERRE. 1993. MODIFYING THE T TEST FOR ASSESSING THE
CORRELATION BETWEEN TWO SPATIAL PROCESSES. BIOMETRICS 49: 305-314.
From Philippe Aubry <paubry@...-lyon1.fr>
> If only one sample is spatially auto-correlated there is no need for aTHIS IS NOTED IN CLIFFORD'S ARTICLE: WHEN ONE OF THE PROCESSES HAS NO
> correction of the classical t test so the p-value you will obtain will
> be statistically reliable (e.g. using a randomization test). But, if the
> two samples show spatial autocorrelation, the p-value calculated in a
> usual way (i.e. for data no spatially dependent) may be very eroneous,
> depending on the magnitude and sign of the autocorrelation in each
> sample. In such a case you need to use a corrected procedure in order to
> evaluate the p-value associated with the observed t statistic.
AUTOCORRELATION, THE STANDARD T-TEST PERFORMS AS WELL AS THE CRH MODIFIED
From Marcia Gumpertz <gumpertz@...>
> I'm not sure what you mean by saying that you produced theI HAVEN'T PURSUED THIS POSSIBILITY AS I DON'T HAVE SAS.
> auto-correlated sample using kriging, but you can use SAS proc mixed to
> fit a regression or analysis of variance model with spatially correlated
> errors. Then you can do a Wald test (like a t-test) to compare two
From "William C. Thayer" <wcthaye@...>
> Have you considered multivariate tests such as Hotelling's T^2? I amDIDN'T PURSUE THIS POSSIBILITY EITHER AS IT DIDN'T SOUND LIKE A SPATIAL
> not sure that this test is appropriate (i.e. do the two sets of data
> represent two populations? Will the test give valid results when one
> set of data is correlated?). The test is designed to consider the
> correlation between the two sets of variables. Wether the two sets of
> data can be treated as two variables measured at the same location (I
> assume that is the case) is another issue that (I think) should be
From Hossein Arsham <harsham@...>
> You may like to look atTHIS REALLY DIDN'T HAVE WHAT I WAS LOOKING FOR.
> Statistical Analysis of Circular Data,
> by N. Fisher, Cambridge University Press, 1993.
> and references therein.
Thanks to the above for replying to my plea for help!
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