Linked Questions

97 votes
1 answer
108k views

When to use an offset in a Poisson regression? [duplicate]

Does anybody know why offset in a Poisson regression is used? What do you achieve by this?
MarkDollar's user avatar
  • 5,975
2 votes
1 answer
4k views

a covariate versus a random effect [duplicate]

I have looked around on cross validated as well as other places but can't seem to find an answer. I'm running a generalized linear mixed-effects model. Y~initial abundance + Treatment + (1|Month) ...
Leo Ohyama's user avatar
2 votes
0 answers
90 views

Why not always use covariate instead of offset in Poisson Regression? [duplicate]

I've just started studying Poisson regression and came across the two models: $$ \begin{align*} \log{\mathbb{E}(count)} &= \beta_0 + \beta_1x_1 + \beta_2x_2 + \log(T) \\\\ \log{\mathbb{E}(count)} &...
John Katsantas's user avatar
1 vote
0 answers
27 views

Simple poisson regression for a death rate [duplicate]

I am trying to regress the death rate for a particular cause of death for 25-30 year olds. My dependent variable of interest is the crude rate, i.e., y = number of deaths of 25-30 year olds/number of ...
Steve's user avatar
  • 661
21 votes
4 answers
22k views

How does a Poisson distribution work when modeling continuous data and does it result in information loss?

A co-worker is analyzing some biological data for her dissertation with some nasty Heteroscedasticity (figure below). She's analyzing it with a mixed model but is still having trouble with the ...
N Brouwer's user avatar
  • 2,163
15 votes
3 answers
20k 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 ...
Vivienne's user avatar
  • 491
14 votes
1 answer
12k views

Identical coefficients estimated in Poisson vs Quasi-Poisson model

In modeling claim count data in an insurance environment, I began with Poisson but then noticed overdispersion. A Quasi-Poisson better modeled the greater mean-variance relationship than the basic ...
Frank H.'s user avatar
  • 586
3 votes
3 answers
8k views

How to estimate and interpret an offset correctly in a Poisson regression?

Assume the following easy example of a glm regression with an offset: ...
MarkDollar's user avatar
  • 5,975
10 votes
3 answers
465 views

Determining statistical significance of linear regression coefficient in the presence of multicollinearity

Suppose I have a bunch of cities with different population sizes, and I wanted to see if there was a positive linear relationship between the number of liquor stores in a city and the number of DUIs. ...
Set's user avatar
  • 1,463
4 votes
2 answers
1k views

Can a variable be used both as an offset and an independent variable?

I am developing a negative binomial regression model that investigates factors impacting the death rate of animals that are fed. The number of deaths was counted over the course of a feeding season, ...
bfuda's user avatar
  • 43
1 vote
1 answer
2k views

Choosing the best family and link function for a GLM

I'm new to GLMs and I need to do several GLM using a kilometric abundance index (non integer, but calculated from a count) as the dependent variable and several habitat traits as the independent ones. ...
arnausc's user avatar
  • 11
3 votes
1 answer
950 views

Why use an offset variable as a predictor instead of just converting outcome to a rate?

I am reporting the results of an analysis where we tested the effect of various demographic predictors on the number of counselling sessions undertaken by participants during a clinical trial. I ran a ...
llewmills's user avatar
  • 2,161
0 votes
1 answer
1k views

Modeling continuous abundance data with a GLM in R: how to select the correct distribution family?

I have abundance data (counts) that I have standardized by area sampled, making them continuous. I would like to explain them with my two independent variables using a GLM but I am having trouble ...
kyle's user avatar
  • 1
3 votes
1 answer
708 views

Transformations for zero inflated non-negative continuous response variable in R

Initially, this was going to be a simple analysis of variance (ANOVA) with a categorical predictor (4 levels) and a non-negative continuous response variable (number of aphids on leaves from four ...
E10's user avatar
  • 91
2 votes
1 answer
676 views

Survival analysis: difference between GLM clog-log family binomial vs GLM clog-log family Poisson

I'm trying to find ways to do survival analysis on data with asynchronous interval-censored outcomes and time-varying covariates. I know that GLM binomial with a complementary log-log link function ...
Wojty's user avatar
  • 75

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