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.

Poisson regression is a regression in which the dependent variable is a count variable. The Poisson regression is a based on the Poisson distribution. In order to apply the Poisson Regression the Equidispersion Property has to be fulfilled: E[X] = Var[X]. If the Equidispersion Property is not fulfilled the Negative Binomial Regression might be a better approach.

Common variants of the Poisson regression are:

  • Zero-inflated Poisson Regression

The dependent variable is a count variable, but many values take on the variable 0.

  • Hurdle model with a Poisson hurdle

The dependent variable is a count variable, but many values take on the variable 0. In contrast to the Zero-Inflated Poisson Regression this is a two step procedure with a hurdle process (e.g. Probit hurdle) and a Poisson regression.

  • Zero-truncated Poisson

The dependent variable is a count variable which can never take on the variable 0. An example are the number of days a person stays in hospital.

Literature:

  • Greene, William H. (2003). Econometric Analysis (Fifth ed.). Prentice-Hall. pp. 740–752. ISBN 0130661899.

  • Paternoster R, Brame R (1997). "Multiple routes to delinquency? A test of developmental and general theories of crime". Criminology. 35: 45–84. doi:10.1111/j.1745-9125.1997.tb00870.x.

  • Berk R, MacDonald J (2008). "Overdispersion and Poisson regression" (PDF). Journal of Quantitative Criminology. 24 (3): 269–284. doi:10.1007/s10940-008-9048-4.

  • Ver Hoef, JAY M.; Boveng, Peter L. (2007-01-01). "Quasi-Poisson vs. Negative Binomial Regression: How should we model overdispersed count data?". Ecology. 88 (11): 2766–2772. Retrieved 2016-09-01. Further reading[edit]

  • Cameron, A. C.; Trivedi, P. K. (1998). Regression analysis of count data. Cambridge University Press. ISBN 0-521-63201-3.

  • Christensen, Ronald (1997). Log-linear models and logistic regression. Springer Texts in Statistics (Second ed.). New York: Springer-Verlag. ISBN 0-387-98247-7. MR 1633357.

  • Gouriéroux, Christian (2000). "The Econometrics of Discrete Positive Variables: the Poisson Model". Econometrics of Qualitative Dependent Variables. New York: Cambridge University Press. pp. 270–83. ISBN 0-521-58985-1.

  • Greene, William H. (2008). "Models for Event Counts and Duration". Econometric Analysis (8th ed.). Upper Saddle River: Prentice Hall. pp. 906–944. ISBN 978-0-13-600383-0.

  • Hilbe, J. M. (2007). Negative Binomial Regression. Cambridge University Press. ISBN 978-0-521-85772-7.

  • Jones, Andrew M.; et al. (2013). "Models for count data". Applied Health Economics. London: Routledge. pp. 295–341. ISBN 978-0-415-67682-3.

  • Wooldridge, J. M. (2002). Econometric analysis of cross section and panel data. Cambridge, Mass: MIT Press. p. 646-656.

  • Cameron, A. C. and Trivedi, P. K. 2009. Microeconometrics Using Stata. College Station, TX: Stata Press.

  • Cameron, A. C. and Trivedi, P. K. 1998. Regression Analysis of Count Data. New York: Cambridge Press.

  • Cameron, A. C. Advances in Count Data Regression Talk for the Applied Statistics Workshop, March 28, 2009. http://cameron.econ.ucdavis.edu/racd/count.html .

  • Dupont, W. D. 2002. Statistical Modeling for Biomedical Researchers: A Simple Introduction to the Analysis of Complex Data. New York: Cambridge Press.

  • Long, J. S. 1997. Regression Models for Categorical and Limited Dependent Variables. Thousand Oaks, CA: Sage Publications.

  • Long, J. S. and Freese, J. 2006. Regression Models for Categorical Dependent Variables Using Stata, Second Edition. College Station, TX: Stata Press.

Software implementations:

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Counting samples seem to not be Poisson distributed, need sanity check

I have an exercise where I have to use Poisson one-way classification / Regression of some data. The data I have is a set of 120 samples grouped the following labels A, B, C, D, E, and F. For each group, there are 20 samples (or 20 repetitions)…
Lars Nielsen
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How to interpret an interaction term in a Poisson regression with change in signs?

I'm building a count model using a Poisson regression. When I run my regression model without an interaction term, both of my main study variables (X1 and X2) show a positive sign. However, when I add an interaction term for these two variables,…
Charlie Glez
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Canonical parameter for Poisson Regression

I was looking at the Poisson regression. Here I find that the canonical parameter is taken to be the logarithm of the rate of the Poisson. I was wondering if there is any reason for considering this as the canonical parameter, rather than the rate…
Devil
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Significance of coefficients in poisson regression

Suppose your significance level is 0.05, and some coefficients are significant and others are not (i.e. some of the p-values are less than 0.05 and others are greater than 0.05). Does this give anything about their importance in relationship with…
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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 (binary outcome) considering some confounders (another…
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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 analyzing Incidence Rate Ratios? I am attaching…
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Frisch-Waugh-Lovell Theorem for Poisson Regression

Consider the Poisson regression model $$ Y=\exp\left( X_{1}\beta_{1}+X_{2}\beta_{2} +\varepsilon \right). $$ Is there something like the Frisch-Waugh-Lovell theorem for this model that would allow me to estimate $\beta_{2}$ by regressing $\exp…
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Sum of two poisson regression on the same predictor

I have two Poisson regression models using same single feature. Model 1 is $$E[\log(y)| x] = a_1 + b_1 \log(x)$$ and Model 2 is $$E[\log(z)|x] = a_2 + b_2 \log(x) $$ When I build Model 3 on $y+z$ like $$E[\log(y+z)|x] = a_3 + b_3 log(x)$$ is…
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Why do we use zero-truncated poisson regression and do not just call outcome 1 outcome 0?

Consider the example of estimating the number of items in the basket of a supermarket shopper. If we assume that a supermarket shopper will always buy at least one item, then a typical approach would be zero-truncated Poisson regression. However,…
Felix H
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Predictions in Poisson Regression

One assumption of the Poisson regression is that the target variable follows a Poisson distribution. Do that also mean that each individual prediction given by a Poisson regression follows a Poisson distribution of parameter lambda = the predicted…
psql
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A little confused about a potential analysis question

This is my first time asking a question here, I have two sets of count data that I want to compare to one another. One set has an excess amount of zeros, while the other does not. My first idea was to use a Zero-Inflated Poisson regression for the…
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Modified Poisson regression

Our study is a cross-sectional study with a total sample size of 30. The dependent variable (presence or absence of MP components in the detected blood clot samples) is a binary categorical variable, with 24 samples testing positive for MP and 6…
zhiheng yi
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interpreting coefficient of Poisson regression, when dependent variable is a count variable

I have a question about the economic interpretation of Poisson regression. What is the economic interpretation of the coefficient when the dependent variable is a count variable? For example, for "Patent Count = a + b × R&D investment + c", what…
Alex
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Poisson Regression output confusion due to categorical variables

I am struggling with the interpretation of my results, specifically the right wording to convey the output. I have looked at multiple examples on this site, but still have not found clarity. I believe my confusion is in the fact that all of my IVs…
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poisson regressions simple and effects regressions (using glmer using glm) producing different result with the same data

I'm using poisson regressions to analyze count data. I have two groups of patients in a clinical trial, and I'm comparing numbers of brain lesions that can be detected on their MRIs at 3 different assessment points. Here is an example of what the…
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