Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

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.

0
votes
0answers
14 views

Offset in NB model produces contradictory results to original data

My (example) data frame is rather simple. I would like to know if there is a difference in numbers between the factors (n=2) within variable X. ...
4
votes
2answers
74 views

Mixed Effect Model - Roadkill hotspot v. coldspot

This problem concerns road mortality. We have 4 highway sections of varied length that were flagged as problem areas for road mortality with large mammals (moose, deer, elk, and even cows). We used ...
1
vote
3answers
91 views

binomial glm with null-hypothesis = 0.33

I have a dataset and need to test if the values are statistical different to 0.33 (=1/3). Flies have the choice between 3 types of berries. So, if they do not care about the type they would lay 1/3 of ...
1
vote
1answer
24 views

Poisson distribution: how to calculate the expected number of zeros in the presence of an exposure term

I have a dataset each with a line for different products, a count of sales and a number of days on sale. I estimated a Poisson regression to predict sales with an offset term of number of days on sale,...
1
vote
0answers
19 views

Can I model incidence per 1000 people per month using poisson regression without an offset or using weights?

I am trying to model incidence rates (number of malaria cases per 1000 people per month) over time. I only have the data in the form of rates per 1000 people per month, i.e. I do not know the total ...
0
votes
0answers
57 views

Weights vs offsets in logistic tree models

I'm interested in the differences in interpretation and functionality regarding weights and offsets in logistic regression trees. In my case, I am using XGBoost trees for logistic regression where the ...
2
votes
0answers
47 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 ...
1
vote
1answer
160 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 ...
2
votes
1answer
29 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 ...
0
votes
1answer
368 views

Confidence interval for mean of Poisson distribution witih observations of different length

I am struggling with calculating a confidence interval for my data using a Poisson distribution. The context is manufacturing process quality control, and I think that a Poisson distribution is the ...
1
vote
1answer
26 views

How to account for different baselines when analysing extremes in time series data

I want to see if Wikipedia articles for topics featured in popular documentaries get a boost in page views on the day the documentary is aired. I then want to see if time on screen is a predictor of ...
1
vote
0answers
375 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 ...
0
votes
0answers
20 views

Include predictions as feature in regression. covariate or offset?

I have a regression setting in which I would like to explore the influence of a given variable on a certain patient condition, given a level of risk for the same outcome, predicted with a more complex ...
1
vote
1answer
242 views

Gamma regression and offset term

I'm testing the effect of soil treatments on root and shoot length of seeds of a species. However the seeds had different sizes, which may affect root and shoot development. I have a measure of the ...
0
votes
1answer
82 views

gamma mixed model with offset and/or weights

I have some continuous positive data $Y_{ij}$ representing accumulated quantities, where $i$ denotes subject and $j$ a state. Patients are transitioning across states sequentially, but not all ...
1
vote
1answer
86 views

Applying offset correctly in an Interrupted Time Series Analysis using segmented regression in GLM in R [closed]

I would like to apply an offset to allow for the population within segmented regression using GLM on count data in R and need to ensure that the formula I am using is correct. Adding offset in 2 ...
2
votes
1answer
643 views

why is XGBoost giving me seriously biased predictions with small nrounds?

I can not put my company data online, but I can provide a reproducible example here. We're modelling Insurance's frequency using Poisson distribution with exposure as offset. Here in this example, ...
15
votes
3answers
696 views

Using glm() as substitute for simple chi square test

I am interested in changing the null hypotheses using glm() in R. For example: ...
1
vote
0answers
29 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 ...
4
votes
1answer
755 views

How to interpret glm and ols with offset

I ran a few glm and linear models with an offset. Each row in the dataset is a healthcare user. The data contains medical payments and icu days of each user between 2000 to 2007. As the number of ...
1
vote
1answer
68 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, ...
3
votes
1answer
222 views

offset in logistic regression to take into account a priori individual probability estimates

I am performing a logistic regression (LR) model on a set of data on which an initial probability estimate for event occurrence, sai $\hat{p_i}^{base}$ has been provided. I have supplementary ...
5
votes
2answers
2k 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 ...
0
votes
0answers
34 views

How to insert temperature and precipitation data on a GEE or GLMM model

I am analysing a data of number of aphids with variation over time (32 avaliations performed every week), area (two areas), and plant position (fixed factor), with 3 replications. Because of that, I ...
0
votes
1answer
400 views

Predict function on negative binomial produces strange fitted values when adding an offset

I have an over-dispersed count dataset and I want to add an offset to my negative binomial on the RHS to create a rate of events for y (see this great answer for ...
3
votes
0answers
103 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 ...
5
votes
1answer
435 views

Offset in Poisson regression when using an identity link function?

It appears that in Poisson regression, using an identity link function means your betas will be rate differences, and using a log link function your (exponentiated) betas will be rate ratios. You can ...
0
votes
0answers
418 views

ITS: Why use an offset to do a Poisson regression instead of modeling a rate from the get-go? [duplicate]

I am doing an interrupted time series analysis in SAS where the outcome is the count of crimes. I have population data for each of the census tracts I am evaluating. Each of the census tracts has ...
3
votes
2answers
2k 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: ...
5
votes
1answer
3k 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 ...
2
votes
1answer
203 views

Recalibration by regressing on intercept only with offset

Consider a risk prediction model developed on one population. When transporting this model to another population, the calibration can be off. There are several strategies for recalibration. One is to ...
2
votes
0answers
51 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 ...
4
votes
1answer
1k 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 ...
4
votes
0answers
306 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 ...
2
votes
1answer
181 views

Need an offset in GLMM even when it is almost invariable and an offset-free model yields a better fit?

I am analyzing frequency data (response variable = no. of seeds produced per plant) by fitting GLMM with a logarithmic link function and a Poisson error distribution. I also have data on no. of ovules ...
1
vote
0answers
22 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 ...
0
votes
1answer
218 views

Set the offset value in lsmeans

I'm using a negative binomial glmm for analysis. The y values of my samples are summed over 12 individual counts of insect mines on leaves of a tree. You can get the data (and session info) from here!...
4
votes
1answer
250 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 ...
3
votes
1answer
84 views

GLM of proportions with offset

I am fitting a glm with a binomial family to consider the relationship between the proportion of trials in which courtship of a female type $A$ occurs (successes) and male genotype (a two level factor)...
3
votes
1answer
2k views

Difference between: Offset and Weights?

I´d like to know the difference between these parameters when I am using GLM/GLMM/GAMLSS/BETAREG. I have observed a lot of published studies using offset, weights and covariates, however I am not sure ...
3
votes
0answers
36 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 ...
1
vote
1answer
150 views

Endogeneity in rate models (poisson/negative binomial with offset)

I might be misunderstanding something, but are poisson or negative binomial models with an offset term for population size (rate models) and independent variables that are rates as well endogenous? In ...
6
votes
1answer
7k views

How to formulate the offset of a GLM

I am trying to build a generalized linear model in R for some count data. Basically I have counted the number of animals per unit after having them presented with a treatment (for all units there was ...
1
vote
0answers
9 views

Unsure about repeated error in Poisson GML offset model [duplicate]

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 ...
10
votes
3answers
2k 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 ...
6
votes
1answer
290 views

Poisson regression: how do number of observations and offset affect variance of betas?

Background: In Poisson regression with an offset, like in this answer, @Hong Ooi writes Your underlying random variable is still $Y$, but by dividing by $\varepsilon$ we've converted the LHS of ...
3
votes
0answers
91 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 ...
3
votes
1answer
745 views

Offset for Negative Binomial Regression

I've constructed a Negative Binomial Regression wherein I predict the number of words an individual will find from a set of seven letters based on the average frequency of words that the set of ...
5
votes
2answers
3k views

Poisson xgboost with exposure

I was trying to model a count dependent variable with uneven exposure. Classical glms would use log(exposure) as offset, also gbm does, but xgboost does not allow for offset until now... Trying to ...
1
vote
1answer
568 views

Poisson regression with offset vs logistic regression

I am thinking to use Poisson regression with an offset variable instead of a logistic regression in case where event is rare, since p (probability of success) is very small and n (sample size is large)...