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mso-paper-source:0;}div.WordSection1 {page:WordSection1;}-->Hello,Iam trying
to take the information from the summary of my best fit logisticregression model
for the occurrence of a high elevation plant spp. and createthe appropriate
equation that will calculate probability of occurrence, given thedata. My
predictors include both continuous variables (slope and a second orderpolynomial
of elevation) and a discrete variable for aspect (warm and cool). Ihave left
unchanged the default contrasts option, so I believe that thefollowing
coefficients were created using treatment contrasts. Myquestion how can I take
this summary output and create the logistic equationthat will allow me to
calculate probability of occurrence. My interests are touse this to spatially
display this info in a GIS environment. I have made adraft equation (shown
below) that uses the coefficients from this summaryoutput, but this appears to
be incorrect – values always return zeroprobabilities. Presumably I need to
adjust the values in some way – but I amunclear as to how to
proceed. Anyguidance would be appreciated! >summary
(model.Slope.Elevation.Aspect) Call:glm(formula= Po ~ Slope + poly(Elevation, 2)
+ Aspect_2, family = quasibinomial) DevianceResiduals: Min 1Q
Median 3Q Max -1.0532 -0.4167 -0.2760 -0.1823
3.3376 Coefficients: Estimate Std. Error t
valuePr(>|t|) (Intercept) -4.577707 0.222406 -20.583 <
2e-16 ***Slope 0.039959 0.003593 11.121 < 2e-16
***poly(Elevation,2)1 8.050898 5.601956 1.437 0.1508
poly(Elevation,2)2 -37.694521 6.297806 -5.985 2.39e-09
***Aspect_2w 0.429229 0.174760 2.456 0.0141 * --- (1/ (1 +
exp(-1 * (-4.577707 + 0.039959*Slope + 8.050898 * poly(Elevation, 2)1 +
-37.694521 * poly(Elevation, 2)2 + 0.429229* Aspect_2w)))))
Brendan Wilson
2530 Alexis Road
Shoreacres BC
Canada V1N 4P6
Ph: 1.250.359.5905
[[alternative HTML version deleted]]
On Sep 6, 2010, at 4:03 AM, B W wrote: <Snipped out formatting detritus and added back many missing speces.>> ->Hello,I am trying to take the information from the summary of my > best fit logisticregression model for the occurrence of a high > elevation plant spp. and create the appropriate equation that will > calculate probability of occurrence, given the data. My predictors > include both continuous variables (slope and a second > orderpolynomial of elevation) and a discrete variable for aspect > (warm and cool). I have left unchanged the default contrasts option, > so I believe that thefollowing coefficients were created using > treatment contrasts. My question how can I take this summary output > and create the logistic equation that will allow me to calculate > probability of occurrence. My interests are touse this to spatially > display this info in a GIS environment.I think you should: -- Read the Posting Guide where you should learn that this is a plain text mailing list and that you need to change the configuration of your mail client. -- Read the help page and read other documentation regarding the use of the predict function.> I have made adraft equation (shown below) that uses the coefficients > from this summaryoutput, but this appears to be incorrect ? values > always return zeroprobabilities. Presumably I need to adjust the > values in some way ? but I am unclear as to how to proceed. > Anyguidance would be appreciated!> >summary (> Call:glm(formula= Po ~ Slope + poly(Elevation, 2) + Aspect_2, family > = quasibinomial) DevianceResiduals: Min 1Q Median > 3Q Max -1.0532 -0.4167 -0.2760 -0.1823 3.3376> Coefficients: Estimate Std. Error t valuePr(>| > t|) (Intercept) -4.577707 0.222406 -20.583 < 2e-16 ***> Slope 0.039959 0.003593 11.121 < 2e-16 ***> poly(Elevation,2)1 8.050898 5.601956 1.437 0.1508> poly(Elevation,2)2 -37.694521 6.297806 -5.985 2.39e-09 ***> Aspect_2w 0.429229 0.174760 2.456 0.0141 * ---You may get predictions at the original data points with: pred < predict(model.Slope.Elevation.Aspect)> (1/ (1 + exp(-1 * (-4.577707 + 0.039959*Slope + 8.050898 * > poly(Elevation, 2)1 + -37.694521 * poly(Elevation, 2)2 + 0.429229* > Aspect_2w))))) > > Brendan Wilson > 2530 Alexis Road > Shoreacres BC > Canada V1N 4P6 > Ph: 1.250.359.5905 > > > > [[alternative HTML version deleted]]David Winsemius, MD West Hartford, CT