Section 10 Count data

In this section, we will talk about models that are appropriate for estimating outcomes that are structured as “count data”– non-negative integer data.

The key characteristics of count data are:

• \(Y\) is not continuous and \(Y_i \geq 0\)
• Typically the count can be small for many observations (not always)
• Describes number of occurrences in a specified time period (the observation period) or space (e.g., per state) (e.g., vetoes during a term in office)

The following supplemental resources may be useful:

• King, Gary. 1998. Unifying political methodology: The likelihood theory of statistical inference. University of Michigan Press. Chapters: 5.5-5.10
• Gelman and Hill Chapter 6. (on Canvas)
• Resources for R related to count data
  • R help for negative binomial from UCLA
  • R help for poisson