[R-sig-ME] Adjusting for random recording intervals in glmer/poisson

Dieter Menne dieter.menne at menne-biomed.de
Thu Jul 5 07:35:01 CEST 2012

In a clinical study, events in patients were observed during multiple visits; on
each visit, a continuous predictor variable for the poisson-distributed number
of events was also available, it is the endpoint of the study.

The following model would be suitable

glmer(nevent~predictor + (1|subj),data=d, family=poisson)

but there is a catch: the recording interval on each day varies randomly, not
related to study parameters, from 30 to 60 minutes. The statistical consultant
at the university recommended the conservative solution to truncate ALL records
to the first 30 minutes, and discard the tails, but the PhD student who did the
study was not too happy to loose all data beyond 30 minutes.

A compromise would be to normalize all data to events/45 minutes (or
median(duration)), assuming that the variance in duration is not too large.

Is there a better way to factor out the nuisance parameter duration?


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