This document discusses organizing count data using a 2x2 contingency table, with examples of how incidence data and incidence density data can be represented in these tables. It notes that some references present the 2x2 table with exposure on top and disease on the left, so it is important to pay attention to the orientation before making calculations. The document also provides notation for elements of a 2x2 table, including exposed and unexposed population totals and total population.

1. 2x2 table
• Count data is typically organized with a 2x2 or contingency table
• Example: with incidence data a/(a+b) = CIe
• What is CI in the total population?

2. 2x2 table
• Incidence density data is also organized with a 2x2 or contingency
table
• Example: a/PTe = IDe

3. 2x2 table
• Note that Stata and the Kleinbaum text book present the
table “backwards” with exposure on top and disease on
the left
• Pay attention to the orientation of the table before
making calculations

4. 2x2 table
Note on notation
–PTexposed = PTe
–PTunexposed = PTu
– PTtotal = PTt
– Will also see applied to measures of disease including
CI, ID