Loading ...
Sorry, an error occurred while loading the content.

GEOSTATS: SUM: spatial t-test

Expand Messages
  • Sarah R. Jacobs
    ... Replies: From Carlos Carroll ... SOME EXCELLENT REFERENCES! CLIFFORD S ARTICLE, ASSESSING THE SIGNIFICANCE OF THE CORRELATION BETWEEN
    Message 1 of 2 , Oct 7, 1998
    View Source
    • 0 Attachment
      Original Question:
      > Is there a spatial equivalent to the non-spatial t-test? I've got two
      > 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.

      Replies:
      From Carlos Carroll <carlos@...>
      > THe CRH modified t-test may be useful. See Clifford et al. 1989.
      > Biometrics 45:123-134, or for an application , see Thomson et al. 1996.
      > Ecology 77:1698-1715.
      SOME EXCELLENT REFERENCES! CLIFFORD'S ARTICLE, "ASSESSING THE
      SIGNIFICANCE OF THE CORRELATION BETWEEN TWO SPATIAL PROCESSES" IS A GREAT
      RESOURCE.
      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 a
      > 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.
      THIS IS NOTED IN CLIFFORD'S ARTICLE: WHEN ONE OF THE PROCESSES HAS NO
      AUTOCORRELATION, THE STANDARD T-TEST PERFORMS AS WELL AS THE CRH MODIFIED
      T-TEST.

      From Marcia Gumpertz <gumpertz@...>
      > I'm not sure what you mean by saying that you produced the
      > 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
      > treatments.
      I HAVEN'T PURSUED THIS POSSIBILITY AS I DON'T HAVE SAS.

      From "William C. Thayer" <wcthaye@...>
      > Have you considered multivariate tests such as Hotelling's T^2? I am
      > 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
      > addressed.
      DIDN'T PURSUE THIS POSSIBILITY EITHER AS IT DIDN'T SOUND LIKE A SPATIAL
      TEST.

      From Hossein Arsham <harsham@...>
      > You may like to look at
      > Statistical Analysis of Circular Data,
      > by N. Fisher, Cambridge University Press, 1993.
      > and references therein.
      THIS REALLY DIDN'T HAVE WHAT I WAS LOOKING FOR.

      Thanks to the above for replying to my plea for help!

      Sarah









      --
      *To post a message to the list, send it to ai-geostats@....
      *As a general service to list users, please remember to post a summary
      of any useful responses to your questions.
      *To unsubscribe, send email to majordomo@... with no subject and
      "unsubscribe ai-geostats" in the message body.
      DO NOT SEND Subscribe/Unsubscribe requests to the list!
    Your message has been successfully submitted and would be delivered to recipients shortly.