[R] Understanding glm family documentation: dev.resids

[Peter Dunn]

Hi all

Consider the  family  function, as used by glm.  The help page says the value of the family object is a list, one element of which is the following:


dev.resids function giving the deviance residuals as a function of (y, mu, wt). 


But reading any of the family functions (eg  poisson) shows that  dev.resids  is a function that computes the *square* of the deviance residuals (at least, by every definition I know of).  Further, the deviance residuals returned by  residuals.glm  are essentially computed as the square root of  dev.resids.

Something seems amiss.  The element  dev.resids  actually seems to compute the deviance residuals squared.  I guess the help file could be changed to read:


dev.resids function giving the square of the deviance residuals as a function of (y, mu, wt). 


...but then,  dev.resids  still seems a misleading label, but that may so entrenched it will never changed.

(By my definition, the square of the deviance residuals is not quite the unit deviance as the weights need to be incorporated differently, but others may disagree.)

Of course, I could be way off track.  I would appreciate enlightenment.

P.




Peter Dunn
Biostatistician
School of Health and Sport Science
Faculty of Science, Health and Education
University of the Sunshine Coast
 
Tel: +61 7 5456 5085
Fax: +61 7 5430 2896
Email: pdunn2 at usc.edu.au
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