## 1785[ai-geostats] RE: F and T-test for samples drawn from the same p

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• Dec 3, 2004
Colin

You need to bear in mind that statistical tests such
as t and F are only testing a very simple hypothesis -
they do not test whether the samples are from the same
population.

The F test is to check whether the standard deviations
differ. If the ore is from the same genesis, it is
likely that the variability will be constant and your
F test will not be significant.

The t test is against the hypothesis that the average
values are the same. That is, one population has a
higher average grade than the other. You can have the
same variability around the mean, but have a zone
where the minerals tend to concentrate at a higher
average.

Even if both tests are not significant, this does not
'prove' that the two populations are the same. You
could have two sets of data with the same mean and
standard deviation and completely different shapes,
for example.

To include the spatial element, you could try a cross
validation approach where one set of samples is the
'actual' values and you try to estimate those from the
other set. This will show up consistent differences in
average between the two as well as differences in
variability.

Strictly, all of the above requires a Normal
distribution but with your not-too-skewed data and
thousands of samples, the Central Limit Theorem should
take care of those problems.

Isobel
http://uk.geocities.com/drisobelclark
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