[R] why does glm.predict give values over 1 ?

(Ted Harding) Ted.Harding at nessie.mcc.ac.uk
Tue Nov 1 00:00:41 CET 2005

On 31-Oct-05 Rohit Singh wrote:
> Hi,
>  This is a newbie question. I have been using glm to perform some
> logistic regression. However, if I take the fitted parameters (as
> part of the glm object) and pass them on the glm.predict function,
> for some test cases I am getting predicted values that are a little
> over 1.  This is a bit puzzling for me, because my understanding
> was that these numbers are probabilities and so should be between
> 0 and 1.
> Thanks a lot! I'd appreciate any help you could provide.
> -rohit

Indeed this should not happen, and probably there is some mistake
in the way you use the predict function (which requires a little

However, it's not possible to point-point what is happening
without seeing a specific case. Can you post an example of the
code you use when this happens? And, if feasible, also an example
of data.

Best wishes,

E-Mail: (Ted Harding) <Ted.Harding at nessie.mcc.ac.uk>
Fax-to-email: +44 (0)870 094 0861
Date: 31-Oct-05                                       Time: 23:00:39
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