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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55 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 ...
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26 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 ...
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9 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 ...
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12 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 ...
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19 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 ...
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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 ...
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10 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 ...
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1answer
49 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 ...
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5 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, ...
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24 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 $...
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75 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 ...
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37 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 ...
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24 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 ...
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1answer
39 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 ...
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10 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 ...
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47 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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18 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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104 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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2answers
213 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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33 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 ...
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14 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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30 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. ...
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2answers
112 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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1answer
31 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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28 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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1answer
66 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 ...
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1answer
241 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 ...
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132 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
111 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
59 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 ...
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1answer
98 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
173 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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143 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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1answer
36 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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1answer
311 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
28 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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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 ...
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479 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
86 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
70 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
145 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
34 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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1answer
286 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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1answer
588 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
206 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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1answer
68 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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80 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
235 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 ...