7
votes
Accepted
When are offsets useful in regressions involving literacy or linguistic data?
Offsets are mostly used for modeling ratios. So ask when ratios do occur in your field. For instance, if you are counting words, but some denominator of interest is not constant (time, some children ...
6
votes
Accepted
Negative binomial for catch data with GAM
For things like this, the Tweedie (family of) distribution(s) is often used. The Tweedie distribution is a family of distributions and contains as special cases the Poisson and gamma distributions (...
4
votes
How to interpret the average rate of NB-GLM when offset is involved?
Number of healthy visits per number of total visits is not a rate, since it has no time in the denominator, but rather a proportion.The distinction may be helpful in searching for an appropriate ...
4
votes
How to interpret the average rate of NB-GLM when offset is involved?
Presuming you're using a log-link, the fit at any given set of predictor-values will be for number of healthy visits per unit of exposure (maximum number of visits per patient), which if I understand ...
2
votes
Parameter estimate interpretations in lm with offset
tl;dr you should probably just compute speed and use it as your response variable; you can do this on the fly in the formula, i.e. ...
2
votes
Modelling catch rates: difference between Gamma and poisson distribution
(OP is probably long gone by now, but ...)
tl;dr you probably want to use a negative binomial model with an offset to account for exposure.
Offsets have a separate purpose from the choice of ...
2
votes
How to adjust for exposure time in a binomial model
You observe if an event occurred or not, but the length of the observation interval varies. If you model the events as a Poisson process, but you only observe if there are zero or more events, but not ...
2
votes
What does one do when the coefficient for the log of the rate estimator for a poisson rate model is very different from 1?
For your dataset, I don't think this can be answered without more context. Why do your variable days vary? If we start with some dataset with individual accidents, ...
2
votes
When are offsets useful in regressions involving literacy or linguistic data?
Some Open Data and Research Questions
Kjetil's answer was already sufficient for my question, but I felt in case it may be helpful to show an example on open data, I would provide a case here. The ...
1
vote
Why is an offset needed in Poisson Regression?
Lambda is the average number of events in a fixed interval (time or space). For example the distribution of chewing gums on each tile on the sidewalk - shamelessly stolen from Wikipedia ;)
Now what ...
1
vote
Predicting with GAM, using an offset
As to why this model
mod2 <- gam(Y ~ covariate1 + covariate2 + covariate3 + covariate4,
offset(log(sampled area)), family=quasipoisson)
does something so ...
1
vote
Understanding emmeans outputs for poisson and negative binomial GLM fitted on count data with or without offset
First of all, the one question I actually can answer is the one about dividing by the mean inflo. This is indeed the case; look at:
...
1
vote
include length text as covariate or offset in negative binomial regression model
It sounds a good solution to include (logarithm of) number of words as an offset in the model. There are similar questions here, have a look at
When are offsets useful in regressions involving ...
1
vote
Ecological count data and offset terms
Q1
The offset term has to be specified (in R at least) on the scale of the linear predictor. Because the canonical (and default) link function in Poisson and negative binomial models is the log link, ...
1
vote
Ecological count data and offset terms
For your first question, see Goodness of fit and which model to choose linear regression or Poisson.
For the second one, I think the answer is NO.
The third one seems to be answered at Predicting with ...
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