Questions tagged [poisson-regression]

Poisson regression is one of a number of regression models for dependent variables that are counts (non-negative integers). A more general model is negative binomial regression. Both have numerous variants.

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Suggestions for an independence test in a complex design

In an experiment I surveyed the effect of two treatments (pre & post) in different species. After every experimental run I tested whether the measured average effect was greater, smaller or not ...
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How to use the parameters estimated by MCMC?

Considering this example, taken from the coursera course "Bayesian Statistics: Techniques and Models", Dataset: ...
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Can very large count outcomes be treated as continuous variables?

I have very little expertise with count outcomes and analysis of them, but I understand that, in general, they cannot be treated as continuous dependent variables for the purpose of analysis due to ...
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ggpredict produces flat fit line for glmmTMB model

I am conducting a step selection analysis of animal movement data using a Poisson model in glmmTMB. The model runs as expected, however, when I use ggeffects to plot model predictions I get a flat ...
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Bayesian Poisson Regression with Gamma Prior Formulas

Are there closed form formulas for the posterior and evidence of a Poisson-Gamma Bayesian regression model? I was not able to find anything that is accessible online. I am not sure for which model can ...
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Variance functions for Poisson, negative binomial

I'm having some trouble understanding how the variance functions of the Poisson or negative binomial tie in to the standard errors on the coefficients. I'm mentioning 2 models because I'm not sure if ...
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How to analyse count data

I have count data on bird abundance obtained from 12 locations. I have summed the abundance for each site as I have been sampling each location twice and there is no significant difference between ...
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Can the offset variable be smaller than the outcome variable in a Poisson model?

I am modeling a number of bags of local crop harvested from a village in a given harvest over time. The village is divided into 48 communities and I have data on the total number of bags of crops from ...
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When to square a variable (age) in a poisson regression?

I cant seem to find a clear answer to my question. I have as a dependent variable a count ( number of times certain companies appeared in the news). One of my explanatory variables is age of the ...
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Generalized linear mixed effects models - Poisson family with log link

When fitting a GLMM with family=poisson(link="log") in lme4, I understand that the coefficients for the estimates of ...
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Why does log-linear analysis seem to ignore the Poisson regression equidispersion assumption?

As far as I understand it, log-linear analysis is based on the use of a Poisson regression. This is what I understood from various online resources, like this online tutorial or this text whose intro ...
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How to retrieve in-sample predictions from BSTS Poisson model

Using the bsts R package to model a time series specifying a 'Poisson' family results in an error when trying to compute insample prediction errors: ...
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How to interpret an interaction in a negative binomial?

I'm investigating the influence of top management team nationality diversity (TMTdiv, continuous between 0-1) and board nationality diversity (Boarddiv, continuous between 0-1) on firm ...
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Which statistical test should I use to see if the month of onset of a disease is random or clusters in the winter?

I have data showing which month a disease started for 119 subjects. The months are represented by 1-12 (Jan - December). We hypothesize the disease more often onsets during winter months. What test ...
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OLS coefficient estimation with Poisson errors

Assume that in this regression $$ Y=\beta_0+\beta_1 x+\epsilon, $$ where $\epsilon$ follows a Poisson distribution. Using OLS, estimate $\beta_0,\beta_1$ and $\text{cov}(\beta_1,\beta_0)$. I am ...
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Stata automatically omits all posiitve or all negative outcomes during poisson panel fixed effectes regression

I am trying to run a poisson fixed panel effects regression using xtpoisson on Stata where my outcome variable is a binary variable. For a majority of my units, the outcome variable = 0 for the entire ...
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Is there a way to correct for degrees of freedom when using a generalized linear model with a Poisson distribution featuring random effects?

I am running a generalized linear mixed effect model with a Poisson distribution to analyse count data. The model has a random effect that takes into account multiple observation obtained by the same ...
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Counterfactual Bayesian survival analysis in pymc

I am trying to determine mortality rates for untreated patients from an observational dataset where treatment has occurred (thus blocking the possibility of further untreated mortality). You can't ...
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Self-Study: Score Statistic of a Poisson

I have been attempting a question on Generalised Linear Models. I thought I understood it but doing exercises myself now, proves otherwise. I have attached an image of the question here, struggling ...
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Derive the non-linear least squares equations for Poisson regression parameters

I have been asked to find the non-linear least squares equations for estimating the parameters of a Poisson regression, and to compare these equations to the MLE equations. More precisely: Consider ...
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How to compare more than 2 groups on the group rate?

I need to compare more than 2 organizations on the number of events each has, controlling for the number of buildings. The number of events per organization is small (0 - 6) and the number of ...
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Winbugs/OpenBUGS code example for Poisson rates?

My data comes from 12 regions. I have the total number of events and the total person-time for each region. For example: ...
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Convert T-values from Poisson regression to Standard Errors

I am trying to summarize results from an article for a review (available for free here, I am looking at table 3), and thus want to find Standard Errors (SE) to compute confidence intervals. The ...
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What better I use for Negative Binomial Regression with library(MASS) glm(family=negative.binomial) or glm.nb?

Hay, im a newbie and still need more learn. I have several question, I'm trying to create a negative binomial regression model using the R and library(MASS). But i'm still confusing what sould I use ...
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Why are GLMMs distinct from GLMs for Meta-analysis of study level data?

Would anyone be able to explain conceptually why GLMMs with a random intercept at the study level are occasionally used for meta-analysis of proportions / counts, when the observations are already at ...
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Comparing the fit of logistic regression model to a poisson regression model

How do we compare the fit of the two models given that the explanatory variables are the same, except the response variable is different? (the response predicts an equivalent thing). We were told that ...
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Is Homicide Victims dataset repeated?

I am studying an example where a Poisson model is applied to the Homicide Victims dataset. The dataset contains survey results of 1308 people who where asked about the number of homicide victims they ...
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PGLM : negative binomial : In sqrt(diag(se)) : NaNs produced

I have a question related to the count model. I am trying to understand whether pickup and drop-offs influence road crash. Therefore, I have road crashes aggregated at the census tract level as my ...
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Specifying distribution in GBM

In the GBM package, we can specify which distribution to use that represents our response variable. I have count data and usually, we specify the distribution as Poisson for count data. But, when I ...
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How to extrapolate a GLM coefficient beyond a single unit change?

This is a basic question but I've never seen it written down. How can I interpret the effect on a dependent variable when there is more than a unit change in the independent variable for a GLM. For ...
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Explanation and simulation of under-dispersion in quasi poisson GLM

I'm currently working on analysis of excess mortality during the pandemic as part of my Master's thesis. I am using UK data, from Public Health England, who use a Quasi Poisson model for expected ...
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How to control for non-response in a Poisson model on survey data

I am analyzing the results of a survey where people nominate other people as connections/friends. People who take the survey can name other individuals who are their friends, or they can submit the ...
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Do poisson regression and exact poisson regression only differ in confidence interval?

The point estimates from the two approaches are the same, right? I plan to use exact Poisson regression for a study, since the events could be sparse after adjusting for a few covariates. Is there ...
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Zero inflation with no zeros in data?

I am investigating feeding rates in great apes. Because I am using count data, I built a generalized linear model with a Poisson link function. So I put the number of items in a bundle as a response ...
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Advantage of Poisson model over Cox PH model for analyzing first event?

For analysis of the first event, I am wondering if Poisson model has any advantage over Cox model, besides some people find rate ratio easier to interpret than hazard ratio? I notice some people use ...
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R package for spatial regression

I want to model counts of a beetle (B) as a function of three continuous dependent variables (PC1, PC2, RL), weighted by a fourth variable (W) using either poisson or quasipoisson regression with ...
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Which regression method to use for zero-inflated continuous target variable and binary predictor variable?

So, i have two columns - first is Income (continous). Almost 96% values of this column is 0's since most entries are not having any income. campaign_support (binary - 1 means yes and 0 means no), ...
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Goodness of fit for Poisson regression with aggregated data

This a folow-up of this question Independence in Poisson regression when used for rates estimation I have a set of thousands of observations. Each relates to an individual, and for eachI have the date ...
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Incidence Risk Ratio for combined risk factor outcome in Poisson regression

I am analysing a large household survey. I specified the survey design based on the survey ids, stratum, weights, and data. So far have been able to get results using the original design. Presently, I ...
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How to estimate population proportions for colored beads in a jar

Suppose I have a jar of colored beads. The jar contains about 15000 of those beads and they come in 10 different colors. I want to know whether there is a a difference between the true population ...
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What is the degree of cell sparsity that Poisson model can tolerate?

For models with no interaction terms, my understanding is that all the marginal cells need to have non-zero counts, in order to have finite estimates. If this minimum requirement is satisfied, will a ...
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Robust standard errors for mixed effects models in R

I understand that you cannot fit a glmer(via "lme4") then test using robust SE estimator. Ie ...
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Is it better to stratify or adjust confounders in the model with small sample size?

My questions is for Poisson models and Cox models. The context is rare/small number of events. We want to adjust for a few categorical confounders: sex, age group, baseline risk, but are not ...
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How to implement change point in JAGS?

I know the package 'mcp' does Bayesian change point, but I want to use base JAGS. Apparently we can't have a random quantity specifying the density of the data. How does 'mcp' do it? Here is my ...
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Using Julian Day and Count Data in the same GLM

I have count data in a poisson distribution. My goal is to determine whether the 5 habitats surveyed (predictor variable) differ in their number of individuals (animals) (the response variable). I am ...
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Converting untruncated Poisson regression effects to truncated effects - theory behind formulae

I am running a zero-truncated Poisson regression in R and the output provides untruncated mean lambdas for effects (i.e. includes values < 1). I have been advised to consider applying one of the ...
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Poisson tree fit an intercept only

Looking at this answer by Achim Zeileis: ...
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Assessing effect modification with Poisson Model

I'm dealing with a cross sectional health survey and I want to test if a Z variable (three-levels categorical variable) is an effect modifier of the association between X (binary exposure) and Y (...
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Is underdispersion problemetic for predictive poisson models?

I am modelling some count data and I suspect my data to be underdispersed. I intend to use the Poisson distribution so that I can use information criteria (BIC) for optimal variable selection. However,...
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Poisson or Binomial distribution for modeling?

I want to model the change in rate of an event in a sampled population. The populations are grouped according to some grouping variable. Each individual observation is of one organism, and the sample ...
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