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.

Filter by
Sorted by
Tagged with
0
votes
0answers
9 views

How to appropriately define counts for a Poisson mixed effects regression

Suppose I have $I$ individuals each contributing count data $X_i \sim \text{Poisson}(\exp(\beta_0 + C_i^\intercal \beta))$. Let $Y_{i1}, \cdots, Y_{i12}$ represent the counts recorded in months $1, \...
0
votes
1answer
22 views

How to include population size in difference-in-differences analysis

I'm trying to estimate the effect of a certain policy intervention on the count of violent incidents in communities which received that intervention, compared to communities which didn't. I'm trying ...
0
votes
0answers
15 views

How to make a stratification in a penalized logistic model with the penalized function?

I use the R package "penalized" and I want to fit a stratified penalized logistic regression model. In the package vignettes, I found: It is possible to include an offset term in the model. ...
1
vote
0answers
125 views

Poisson regression with offset - help with fit and visualization

My goal is to understand the relationship between the number of worms found in a plot of land and the percent silt that makes up the soil. The plots of land have been investigated to different extents ...
0
votes
0answers
17 views

using per capita or raw counts for epidemiological regression analysis

I have two datasets. To simplify, they look something like this: ...
5
votes
2answers
272 views

Does offset always have to be on log scale with NB GLMM?

I'm using a negative binomial GLMM with R package lme4 to detect differences in time mothers spend feeding before and after birth (inf_cat). ...
0
votes
0answers
38 views

How to plot a poisson model with offset?

I fitted a glm poisson with an offset term (in R) to my data and found a relationship between predictor and response variable. Now I would like to create a scatterplot with my original data in ...
1
vote
1answer
24 views

Do offsets consume degrees of freedom?

In a model with some offset variables (variables with pre-determined regression coefficients), do these variables consume degrees of freedom, with regard of e.g. information criteria? Pro: You can ...
1
vote
0answers
21 views

GLMM: How to impose a specific parameter (intercept or slope) for the model?

Good afternoon, I would like to know if it’s possible and how to specify parameters in a GLMM. Let’s take the example of a GLMM with random intercepts. In the following equation, the vector of fixed ...
0
votes
0answers
19 views

AIC difference after adding offset in negative binomial in R

I'm quite confused about how R calculate likelihood/AIC in glm.nb after adding the offset. In this example, the regression coefficients are the same but the AICs ...
1
vote
0answers
22 views

Modelling catch rates: difference between Gamma and poisson distribution

I am confused about the difference between modelling counts (i.e. catch) using a poisson distribution with an offset (i.e. effort) and modelling catch per unit effort using a gamma(link=log) ...
2
votes
1answer
49 views

Can I partial out covariates with true coefficients known in Logit?

Suppose the model is $$ \ln(\frac{P_{ij}}{1-P_{ij}}) = X_{ij}\beta_0 + A_i + A_j + \epsilon_{ij}, $$ The unit of observation is at $ij$ level, and $A_i$ and $A_j$ are coefficients on the dummy for ...
3
votes
1answer
69 views

Understanding offsets for continuous variables

I'm currently trying to write a linear model with data from some behavioural experiments with termites. I started to read Ben Bolker's "Ecological Models and Data in R", which has been a ...
0
votes
0answers
53 views

Modelling overdispersed rate data using a negative-binomial distribution

A quick overview of the analysis I'm wanting to do: I am wanting to analyze the relationship between habitat factors and the capture of my research species over a network of traps, in order to be able ...
0
votes
0answers
57 views

Can weights be used in place of offset in Tweedie model

I have seen evidence that Poisson regression can be run with either offsets or weights for time and both give the same results. However, I have noticed that the same is not true for Tweedie. I have ...
0
votes
0answers
15 views

Is it appropriate to use an offset function in a model to control for a constant?

I have data from 10 aerial surveys completed over 20 years. I want to determine if my study species has any habitat preferences. To do this I used a mixed generalized additive model with my variable ...
0
votes
1answer
69 views

mvabund package can't handle offsets?

I have a set of fish data from a lake. I am trying to see whether the local fish community differs depending on the location within the lake (North, East, West), the presence of an island at the ...
0
votes
0answers
8 views

Controlling for two variables

I have a continuous response, "runoff volume" (Y), in a study of hydrology. But, the response depends on "area size" and "intensity of rainfall". If I want to calculate ...
0
votes
0answers
16 views

How add a fixed offset term to account for a known effect in a repeated measures mixed model?

I'm running a lmer with a continuous outcome TestY measured in each visit a participant makes to the study i.e. a longitudinal repeated measures analysis. The ...
1
vote
1answer
95 views

How to handle a constant parameter in a Poisson regression?

I have a Poisson regression model with rate, $\lambda$, defined as $ln (\lambda) = \alpha + \beta + \gamma$. Here $\alpha$ and $\beta$ change and $\gamma$ is 0.5 for each observation. $\gamma$ is ...
0
votes
0answers
8 views

If I insert the exposure time as a regressor instead of as an offset in a Poisson regression, should I also weight for it?

I have, as outcome, the number of contacts with a medical service per week. Normally, in a Poisson regression, one should use an offset for the number of working days in the week. However, in my case, ...
3
votes
0answers
30 views

Variance of negative binomial given an offset

Given observations $Y_1, \ldots, Y_n$ from the negative binomial distribution, $NB(\mu, \theta)$, and assume that we model the mean with a GAM: $$\log E(Y_i) = \log \mu_i = \log t_i + f(x_i),$$ where $...
1
vote
0answers
14 views

Interpretation of quasi poisson regression with offset

I am trying to find out how to correctly interpret the coefficients for a Poisson regression. My main outcome of interest is the number of antibiotics prescribed (count) or the rate of antibiotics ...
1
vote
0answers
102 views

Incorporate offset into mgcv GAM smoothing

When developing mortality models, I often have the following problem: I have a prior/base rate table and mortality experience data from a population of interest, and I need to develop factors on top ...
2
votes
0answers
65 views

How to adjust for exposure time in a binomial model

I have several binomial (logit) models that predict the probability of various binary outcomes (e.g., incurring any costs for health care treatment, having a chronic disease). My case and control ...
0
votes
0answers
25 views

Offset not working well in negative binomial

I have been trying to add an offset to a negative binomial model. My response variable is the number of movements an animal makes. The videos that are used to obtain these measures vary in length, so ...
1
vote
1answer
75 views

Best GLM to model a random variable that represents a count over a non-fixed interval of time

The random variable on which I am seeking to fit a GLM is the number of times a patient has a blood glucose level measurement above a specified threshold before they are escalated onto a stronger ...
1
vote
0answers
16 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 ...
0
votes
1answer
56 views

Why do results differ with and without offset in Poisson regression?

I have a dataset with counts of preterm births for five years by county. I am running analyses to see whether contaminant water concentration levels for each county for each year predict preterm ...
2
votes
0answers
158 views

Offset vs weigths in GLM

I was wondering from a technical perspective what approach I should follow in this modelling problem I have. I have a target variable Y which is a continuous random ...
0
votes
2answers
383 views

Post hoc analysis after GLM model using count data and offset

I have ecological count data across 15 sampling sites. The count data has a Poisson distribution and I have included an offset for "area_searched", which is the m^2 of each sampling site as ...
2
votes
0answers
34 views

Using Offset in Binomial/Logit GLM for Exposure Years? [duplicate]

I am building a GLM Model that predicts whether there will be a claim in a certain policy or not. So target variable is either 0 or 1, so my choice of GLM was Binomial, and link function was Logit. In ...
0
votes
0answers
32 views

How to include offsets of 2 variable in one linear model

I've been conducting some research on recruitment of fish and fish survival in estuaries. I'm analysing recruitment and mortality against environmental variables such as temperature and river flow. ...
2
votes
2answers
175 views

How do you fix one slope coefficient in an interaction term?

hoping someone can help me with what (on the face of it) appears to be a relatively simple problem but which I can't current code out. Basically, I would like to fit a GLM in R with a simple two-way ...
1
vote
1answer
37 views

Finding the difference between a normally distributed random number and randn with an offset using Kolmogorov-Smirnov test and Chi-square test

A normally disturbed random number is generated using randn function in Python. The KS test and Chi-square test is performed to check if the generated numbers belong to a Gaussian (zero mean, unit ...
0
votes
1answer
108 views

Multicollinearity for Offset Variable?

In a Poisson model, do we need to check for multicollinearity between the offset variable and other covariates? For example, if I offset by population size, would it be problematic to include ...
1
vote
1answer
355 views

log-offset in rpart regression tree

I have understood that one commonly adds log(exposure) as an offset in the formula for GLMs, when dealing with poisson distributed rate data. I am dealing with insurance claim data where I want to ...
1
vote
0answers
157 views

Ecological count data and offset terms

Problem: When using GAMs to model ecological count data (e.g. fish counts) using Poisson or negative-binomial distributions, the response variable is raw counts and the offset (e.g. log-transformed ...
0
votes
1answer
154 views

Zero offset values, glmm poisson/negative binomial distribution with

I have a data set that consists of video observations of carpenter bee nests under three treatments: a control, mothers removed and mothers and worker removed. I have counts of twenty behaviours as ...
3
votes
1answer
60 views

Including a variable in a regression but NOT estimating its coefficient

I came across a curious problem trying to replicate a paper. The results in the paper were estimated using Eviews, which I am not familiar with. I noticed the author specified (by formula) and ...
1
vote
1answer
130 views

Count Modelling and Rates and Zero Inflation

I am looking for some help modelling overdispersed (zero-inflated negative binomial) count data as a rate. I want to model the survivability of villages in different municipalities given guerilla ...
2
votes
1answer
237 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 ...
1
vote
0answers
204 views

What actually happens when we model a frequency instead of count (POISSON GLM)

First of all, I am using R. I know that we can model a frequency-response variable with a poisson regression, if we remember to weight it, so that the variance doesn't get affected by it. I am not ...
0
votes
1answer
50 views

How to account for adjustment of categorical parameters in R poisson regression

I recently read about poisson regression in R and also about the offset that can be set, as for example described here. If I understand correctly, this can be used to account for continuous ...
2
votes
1answer
413 views

May "offsets" be used in mixed-effects poisson regression?

Mixed-effects poisson regression studies counts for example of the incidence of a disease given the individual's random-intercept/slope. Mixed-effects regression studies individuals rather than ...
1
vote
1answer
31 views

May "offset" in poisson regression be a constant? [closed]

Let's say I'm trying to model the incidence of disease per 1000 people. I have data where people are id'd for example 1001,1002,1003,.... am I allowed to specify the offset as ...
0
votes
1answer
30 views

Explanation of the model used in the following glm commands

In my textbook, the following two models were used. I understand the theory of glms, but I'm not too sure as to the specifics of the options and parameters you can play with in the R glm function. I ...
2
votes
0answers
523 views

specifying random effect as offset in logistic glm (R)

I am working on a measurement error model for presence/absence data using a variant of a Monte Carlo EM (MCEM) algorithm for model fitting. As part of this approach, I simulate random effects by ...
3
votes
1answer
111 views

Does the inclusion of a model offset convert predictor variables from counts to rates?

Does the inclusion of a model offset in Poisson or logistic regression convert predictor variables from counts to rates? Or does it only convert response variables from counts to rates? I understand ...