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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21 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 ...
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8 views

Use offset variable instead of modelling y as a proportion

Most questions regarding using offset variable relates to rate or take the count per unit time. I would like to model the number of daily hospital admission (general ward, ICU etc.) from emergency ...
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29 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 ...
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34 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 ...
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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 ...
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10 views

GEEGLM or NEGBIN with offset person time follow-up

I am analyzing number of hospitalizations in 5 years of followup for a cohort of subjects. Some of these withdraw before the end of study. How can I consider it in a model for count data? Is it ...
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33 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 ...
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26 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 ...
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25 views

GLM cell counts vs. offset with or without percentages

I have counted in a defined cell population (all_cells) the number of positive cells with marker A (cell_counts_a) and the ...
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83 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 ...
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1answer
48 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 ...
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1answer
45 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 ...
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1answer
74 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 ...
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84 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 ...
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33 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 ...
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31 views

Offsets variable subjects and behaviors

I have a set of behavioural data. It consists of about 600+ 50 mins long observations within 35 different bee nests, with many different numbers of observations per nest, and variable numbers of bees ...
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51 views

compare two GLM models on test set using deviance reduction with offset prediction

I'm trying to compare the goodness of fit of two GLM models of claims frequency, one "baseline" and one with some more variables we recovered from external sources. The approach I'm following should ...
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1answer
154 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 ...
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1answer
21 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 ...
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29 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 ...
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57 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 ...
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403 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 ...
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1answer
47 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 ...
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1answer
56 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 ...
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1answer
74 views

Multiple linear regression LSE when one of parameter is known

Question is the following: For analyzing the observed data, the following regression model \begin{eqnarray} y_i=\beta_0+\beta_1x_{i1}+\beta_2x_{i2}+\beta_3x_{i3}+\epsilon_i \end{eqnarray} is ...
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1answer
33 views

Admissions per year before and after antibiotics?

I need to compare hospital admissions per year before and after the introduction of antibiotics in 100 patients (antibiotics introduced at various time points in the past). Eg. Before antibiotics: ...
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102 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 ...
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338 views

Use the offset or use rates as dependent variable in Poisson regression

I'm using a data set of an insurance company, and I want to model the number of claims (counts) as a dependent variable (number of insurance claims, nb_sinistre in this data set). In R I use a glm ...
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2answers
155 views

How do I fit models with predetermined covariates?

I'm trying to fit a multiple linear regression model. It has 10 variables, 2 of which are specified (e.g. $\beta_4 = 0.5$, $\beta_7 = 0.77$). How do I go about fitting this in R? I need to find the ...
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30 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 ...
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61 views

Is an offset term necessary for a count model of a behavior where subjects determine trial length?

We are modeling data from a behavioral study in which subject pairs' conversations are coded for specific types of utterances (say "Type A"). Subjects decide when their trial is over and we count Type ...
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47 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 ...
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1answer
140 views

Overdispersed poisson-distribution and offset --> standard errors?

I am modeling count data using R and doing a fixed-effects/random-effects model and thus limited on functions and therefore cannot use a quasipoisson model or negative binomial distribution, but ...
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2answers
410 views

What type of data is needed for offset in a Poisson regression model - R

I am trying to do a Poisson regression using the following data, where infant deaths are shown per year for both North and South England. ...
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1answer
39 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 ...
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1answer
43 views

Comparison of paired count data between two treatment periods with different length of follow-up

I am currently using SAS 9.4 to carry out a retrospective analysis of patients who switched from drug A to drug B. I am interested in assessing the hospitalization counts before and after switch to ...
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438 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....
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46 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 ...
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1answer
126 views

Should I include offset in null negative binomial model for comparing to full model?

I'm modeling how various landscape and ecological factors affect the I'd like to evaluate how well my negative binomial model performs over the null. I've specified an offset variable in my model to ...
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1answer
191 views

Offset term in negative binomial regression

I am fitting a simple negative binomial regression model with (Yearly cancer death ~ Offset (Size of population) + Age + Household income). I used the offset term because I want to compare the yearly ...
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2answers
819 views

Residual Deviance and degrees of freedom - Negative Binomial Distribution

I am trying to model count data using python's statsmodels module (Beer's sold at a football stadium as function of visitors, "tilskuer", and weather data). ...
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1answer
99 views

Logistic regression with coefficients penalized to other numbers

When you penalize logistic regression using l1, l2 or both penalizations, the coefficients are penalized towards 0. I would like to do the same thing but penalizing the coefficients towards other ...
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1answer
412 views

Negative Binomial Regression: Offset Variable and Dispersion Parameter

My case is that previously it's assumed that the counts of events follows a negative binomial distribution, and the annualized exacerbation rate is 1 with a dispersion parameter of 1.5, and all 500 ...
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2answers
137 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 ...
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3answers
393 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 ...
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1answer
186 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,...
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1answer
134 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 ...
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197 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 ...
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1answer
878 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 ...