[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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 One of my students noticed that the "F-test" in r.regression.line does not
 seem to be calculating F, but instead calculating -(R squared).

 For example, from the Spearfish demo data,

 {{{

 r.regression.line map1=elevation.dem at PERMANENT map2=slope at PERMANENT
 y = a + b*x
    a (Offset): -16.675093
    b (Gain): 0.020833
    R (sumXY - sumX*sumY/N): 0.481666
    N (Number of elements): 2611107
    F (F-test significance): -0.232002
    meanX (Mean of map1): 1353.724982
    sdX (Standard deviation of map1): 176.754565
    meanY (Mean of map2): 11.527723
    sdY (Standard deviation of map2): 7.645157

 }}}

 0.481666^2 = 0.232002

 I haven't checked, but this probably affects all versions of GRASS

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