[GRASS-dev] [GRASS GIS] #1668: r.regression.line F-test incorrect
GRASS GIS
trac at osgeo.org
Thu May 31 02:10:58 PDT 2012
#1668: r.regression.line F-test incorrect
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Reporter: cmbarton | Owner: grass-dev@…
Type: defect | Status: new
Priority: normal | Milestone: 7.0.0
Component: Raster | Version: unspecified
Keywords: | Platform: Unspecified
Cpu: Unspecified |
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Comment(by mlennert):
Replying to [comment:2 cmbarton]:
> These DO give VERY different values. For slope vs. elevation in my
Spearfish example, the current equation gives a value of -0.2320019531,
while the revised equation gives a value of 1.02410689008565E-006.
>
>
http://www.weibull.com/DOEWeb/hypothesis_tests_in_simple_linear_regression.htm
defines
> F = SumSq Regression /( SumSq Errors / (count - 2))
Yup, sorry, in my proposal another set of parentheses was missing. It
should be:
F = R * R / ((1 - R * R) / (count - 2));
where
R*R = SumSq Regression
1-R*R = SumSq Errors
which in your example gives you a value for F = 788781, i.e. a probability
that there is a relationship so close to one that most software will
probably just give you 1 after rounding.
Again, I can commit this, but would like to have someone more versed in
statistics confirm.
Moritz
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Ticket URL: <http://trac.osgeo.org/grass/ticket/1668#comment:3>
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