# 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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### Transformation of confidence limits of Poisson Log linear glmm

I fitted a Poisson log linear model of the form Y ~ poisson(lambda) log(lambda) = mu + beta1X1 + beta2X2 I obtained the estimates and confidence limits ...
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### Interpreting estimates in a Poisson regression

I know similar questions have already been answered but in this particular case I need some additional help. I am working with this data set: https://github.com/proback/BeyondMLR/blob/master/data/...
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### 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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### 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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### GLM to use for non-negative real data or percentage data?

I would like to do a regression model for the following responses/dependent variable: number of cases at the hospital emergency department waiting time from registration to consultation percentage of ...
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### Independence models in sampling 2 way contingency table?

I have just went through a lecture on sampling 2-way contingency table data via multinomial, product multinomial and Poisson sampling. The associated reduced models for each sampling are the ...
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### Can IWeights Be Used as a Substitute for AWeights When Using XTPOISSON in Stata?

I am using a Poisson-regression fixed-effect model to estimate the effect that automatic voter registration had on the number of new Oregon voters in the 2016 general election. Since Stata does not ...
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### How do I tell if word frequencies are changing over time?

I have a collection of texts that span about 1000 years. I am interested in the frequency of a particular word in these texts. Specifically, I want to know whether the frequency of the word increased ...
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### If outcome is a count from a finite number of possible instances, is binomial or poisson regression more appropriate?

I have an outcome variable that is the number of criteria participants meet for a diagnosis of substance dependence. The minimum number of criteria participants can meet is 0 and the maximum is 11. So ...
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### How to do a ppml regression with fixed effects

I am estimating a gravity model aiming at evaluating how patents can affect trade patterns. I am using a ppml model using the glm command in R. As identification strategy, I am using fixed effects ...
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### Interpreting results from a Poisson and Quasipoisson model

I used Poisson regression model to model how count of user actions on a website (dependent variable) are explained by website content (independent variables). The dependent variable distribution is ...
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### Negative infinity produced when computing log-likelihood in Poisson Regression R

I am trying to compute the log-likelihood in a Poisson regression in R. However, my computation produces negative infinity values for some observations. This is my code: ...
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### Crude incidence rate ratios giving different results to conditional Poisson regression model

I am analysing the treatment effect of a compound, namely the rate at which an event occurs during treatment. I have calculated the crude incidence rate ratio for a group of subjects, each of whom has ...
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### Basic R-Squared in Poisson Regression

I have read one cannot/should not calculate the basic R-Squared used in linear regression for a Poisson generalized linear regression model. It is logical to me that one cannot determine the basic R-...
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### Why can we use a deviance test for a quasi likelihood models?

I know that the reason why you don't obtain a value for AIC if you fit a quasi-likelihood model is because a quasi-likelihood is not a real likelihood, and to obtain a value for AIC, you need a real ...
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### Interpreting Poisson regression analysis

I ran my data through R and got these results. I wanted to ask about the meaning of the results. Could it be that one variable is not significant when looking at the entire model, but significant when ...
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### Negative Binomial or Poisson regression?

My dependent variable (count) shows signs of overdispersion (mean 2.50, Variance 6.60), which led me to use a negative binomial model. This seems to fit better compared to the Poisson regression (...
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### Testing for endogeneity in a negative binomial model

I'm trying to fit a negative binomial model to my data because the dependent variable exhibits overdispersion. However, one of my reviewers is insisting that I also test for endogeneity. He or she is ...
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### How can a relationship be U-shaped when both linear and quadratic terms are positive and significant?

I have a predictor variable that ranges between 0-1, transformed to natural log due to multicollinearity and modeled with fixed effect negative binomial. Both the linear (B=9.9, St Error = 2.71, p<...