# 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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### Analysis of survival data using binomial GLM with offset

We are interested in determining whether there's an association between frequency of screening visits and cancer outcomes and whether that differs by race. We have Medicare data to analyze this. ...
652 views

### How a tweedie glm handles an offset?

I am trying to fit a model with a glm using a tweedie family. I use a index parameter p between 1 and 2 to get a compound Poisson Gamma distribution to fit my data. But I want to use an offset only on ...
163 views

### How does Poisson regression (with an offset) relate to Logistic regression?

I have some data I am trying to analyze of how often someone has chosen a given option (which I'll call choice A) vs not choosing it (which I'll call choice B) during a 6 month period. Each subject ...
186 views

### How can I account for different sampling effort in my GLMM Poisson regression using glmer() - easily reproduced example inc

I've been grappling with my dataset for what seems like a very long time now. Hope someone can point me in the right direction. I would like to know how to account for the differing sampling effort ...
462 views

### Can a GLM with exponential response distribution be transformed into a Poisson regression instead?

Given the following generative model $$T | \mathbf{x_i} \sim \operatorname{Exp}(\lambda_i)$$ $$\ln(\lambda_i) = \beta_0 + \beta_1 x_1 + \beta_2 x_2 + \dots$$ That is: I have observations of ...
41 views

### What does one do when the coefficient for the log of the rate estimator for a poisson rate model is very different from 1?

Let's say we have "number of accidents" as the response in a poisson regression model. One of the predictors is "number of days." Naturally, we expect more accidents to occur over more days, so it ...
132 views

### How to account for patterns in GAMM residuals due to the addition of an offset?

I have been wrestling with some model problems for a few weeks now and would like some help. I am trying to determine whether fish catch rates have changed following an event using GAMM. Because ...
27 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 ...
27 views

### Why does adding an offset change the coefficients in a Poisson regression?

Suppose I run Poisson regressions but every time the only difference is the offset. Why are my estimated coefficients different? The offset is just like any other predictor in a linear model, the ...
230 views

### How does offset in XGBoost is handled in binary:logistic objective function

I am working on a mortality prediction (binary outcome) problem with “base mortality probability” as my offset in the XGboost problem. I have used gbtree booster and binary:logistic objective function....
648 views

### Offset option in Proc Logistic (SAS)

What difference does it make in estimation of model equation if a variable is specified in offset option in proc logistic? I know, if I specify a variable in offset option; the variable will be ...
67 views

### Count data with “double offsets”?

I am looking into race and homicides in the USA, 1995-2016. I want to look into "trans-race" (victim and perpetrator different races) homicides by race and year. However I want to also include effects ...
67 views

### Is an offset valid or is it endogenous in this count modeling scenario

Theory seems to indicate that an offset should be included in count models if groups are observed for different lengths of time or if they have different levels of exposure. Suppose we are observing ...
139 views

### Correlation between offset and predictor in count data

I am fitting a Poisson model that requires an offset term to account for sampling effort. However the offset term is highly correlated with one of the linear predictors that is central to my ...
570 views

### How to calculate robust standard error with offset?

I think the default vcovHC in R's sandwich package does not handle offsets in Poisson models. We see this because robust (heteroscedasticity consistent) standard ...
887 views

### How to estimate an mlogit (R package) model with a fixed (offset) variable

I am trying to estimate a multinomial logit model using an offset variable with the mlogit package of R Using the syntax here [https://stat.ethz.ch/R-manual/R-devel/library/stats/html/formula.html] ...
232 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 ...
38 views

### Account for the number of Bernoulli trials in the response and selected predictors of GLM?

I have sampled animals at a number of sites and time points. Each site is sampled up to 4 times a year and is sampled over multiple years. At each site*time ...
723 views

### GLM with averaged-count data - Poisson? Negative Binomial? Offset?

I am trying to construct GLMs to explore the relationship between woodpecker abundance and 9 predictor variables (tree density, canopy cover, and so on). My data were collected as counts of ...
50 views

### Using an offset term with panel data and unexposed controls

I'm evaluating the effect of a policy change on a count outcome across a number of units over time. I have panel data for 300 units over 20 time periods, with roughly 20% of units exposed to the ...
50 views

### Negative Binomial Regression model discrepancies

In a table, I've got total plant Counts (C), previous yr plant counts(PC), and multiple weather predictors(W; continuous data). The objective is examine the relationship between counts (C) and various ...
185 views

### Poisson model with multiple time offsets

I am trying to model health outcome rates by flu-season. I.e. hospitalization rates in good flu-years versus bad years. I am working with individual level nursing home resident data from ...
144 views

### Logarithmic offset + Scaling Counts + Multiplying by Scalar + Poisson Regression

I am working with a contingency table where I know that the population sizes from which the counts are derived are very different. From what I have been able to gather, an appropriate way to adjust ...
360 views

### Exposure variable negative binomial

I am using a negative binomial regression to analyse the amount of purchases per day for different products. When products are available for a different amount of time, (for example product A is ...
167 views

### Regression Model - forcing a coefficient/effect to be 1

Currently we have a linear model which includes 3 independent variables and the dependent variable "Y" which is the predicted values (range from -0.5 to 2000) from the model. Now we want to leverage ...
847 views

### Analysis of rates and post hoc test with offset variable using glmer.nb

I am investigating variation in pollinator visitation rate (number of visits per inflorescence) with treatment and time category as fixed factors. Block is a random factor. Following Zuur et al. (2009)...
100 views

### Confusion about the kind of offset-value for this non homogenous poisson-process

Suppose that I observe $M$-times this kind of table: ...
20 views

### Beta regression or logistic regression with an offset term?

I have a dependent variable (DV) that is a proportion that is bounded by [0,1). Initially I was considering using a beta regression to model the relationship between this proportion and two other ...
27 views

### Poisson regression with custom offset and link

I have the following model $$Y \sim \operatorname{Poisson}\left(\frac{1}{1+\exp(\beta X)} E\right)$$ In other words, I have count data for Poisson process with exposure E and rate given by the ...
25 views

### Log-linear model for contingency table with no fixed count

I have table of counts of born children with four two-level factor variables (mother smoker/nonsmoker, child born dead/alive, ..). I would like to use log-linear model to understand interactions of ...
19 views

### Can I use Poisson regression to model prevalence ratios if I only have information on events?

I often used Poisson regression models to estimate prevalence ratios. However, in these cases my data contained information on the whole population, including events (1) and non events (0). ...
30 views

### Statistical specification for a Regression with continuous finite range count like data

I am interested in explaining what kind of personal characteristics and work environment variables are associated with sickness absenteeism. My dependent variable is the total number of days a given ...
47 views

### Interpretation of average marginal effect for proportion outcome in Poisson model with offset

To see the association of malaria prevalence with village level risk factors, I ran a Poisson model in r with the prevalence of malaria(y) as a dependent variable, altitude(x1) and Forestation(x2) as ...
42 views

### How to fit a gls model with a known slope

i want to fit a gls model (from nlme package) with a specified slope, so i can get the computed intercept for the best fit. I tried to set the slope with an offset. Althogh it works fine with lm, it ...