[R] Understanding glm family documentation: dev.resids

From: Peter Dunn <PDunn2_at_usc.edu.au>
Date: Thu, 13 Nov 2008 09:30:21 +1000


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
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Email: pdunn2_at_usc.edu.au
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