[GRASS-dev] [GRASS GIS] #1668: r.regression.line F-test incorrect

[GRASS GIS]

#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 mmetz):

 Replying to [comment:3 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.

 You can compare to the grass7 addon r.regression.multi whose results are
 identical to those of R.

 Markus M

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Ticket URL: <http://trac.osgeo.org/grass/ticket/1668#comment:4>
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