Mathematics
Poisson Regression for Modelling Count Data
Quick fact
Poisson regression assumes that the variance of the count equals its mean, which is a strong restriction known as equidispersion—yet real data often show overdispersion, requiring extensions like the negative binomial model.
Why this is interesting
Have you ever tried to predict the number of rainy days in a month or the number of accidents at an intersection? Ordinary linear regression can give predictions that are negative or nonsensical.