# Questions tagged [offset]

A variable with a fixed coefficient of 1. Offsets are commonly used in Poisson regression to allow the modeling of rates instead of counts.

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### When to use an offset in a Poisson regression?

Does anybody know why offset in a Poisson regression is used? What do you achieve by this?
21k views

### Using offset in binomial model to account for increased numbers of patients

Two related questions from me. I have a data frame which contains numbers of patients in one column (range 10 - 17 patients) and 0s and 1s showing whether an incident happened that day. I'm using a ...
30k views

### Where does the offset go in Poisson/negative binomial regression? [duplicate]

(First of all, just to confirm, an offset variable functions basically the same way in Poisson and negative binomial regression, right?) Reading about the use of an offset variable, it seems to me ...
7k views

### In a Poisson model, what is the difference between using time as a covariate or an offset?

I recently discovered how to model exposures over time using the log of (e.g.) time as an offset in a Poisson regression. I understood that the offset corresponds to having time as covariate with ...
2k views

### How is a Poisson rate regression equal to a Poisson regression with corresponding offset term?

I do not understand the role of weights in "weighted Poisson regression". What exactly is being weighted? Is it the contribution of the observation to the log-likelihood of the model, or something ...
5k views

### Should I use an offset for my Poisson GLM?

I am carrying out research to look at differences in fish density and fish species richness when using two different underwater visual census methods. My data was originally count data but then ...
4k views

### Can Weights and Offset lead to similar results in poisson regression?

In "A Practioner's guide to Generalized linear models" in paragraph 1.83 it is stated that: "In the particular case of a Poisson multiplicative GLM it can be shown that modelling claim counts with ...
919 views

### Scaling vs Offsetting in Quasi-Poisson GLM

I recently modeled insurance claim frequency assuming a Quasi-Poisson distribution in R. My frequency dependent variable was calculated, in advance of modeling, as the number of claims per underlying ...
5k views

### Difference between offset and exposure in Poisson Regression

Exposure and offset are two techniques often used in Poisson regressions by actuaries to predict claim frequency . From my understanding, offset and exposure are the same things, so I don't ...
7k views

### Binary Models (Probit and Logit) with a Logarithmic Offset

Does anyone have a derivation of how an offset works in binary models like probit and logit? In my problem, the follow-up window can vary in length. Suppose patients get a prophylactic shot as ...
1k views

### Using glm() as substitute for simple chi square test

I am interested in changing the null hypotheses using glm() in R. For example: ...
5k views

### Offset in Logistic regression: what are the typical use cases?

Offset is commonly used in Poisson regression to take into account different exposure (different time periods for instance): offset = log of exposure Question: ...
673 views

### Is it possible to use two offsets?

I am doing negative binomial linear mixed model using lme4 package in R. My question is whether or not there is a way to put two ...
558 views