Let’s start to look at the some of the ways we can analyze and summarize surveillance data. First, let’s look at analyses done by person. In order to target disease prevention programs to the most appropriate population groups, cases should be characterized by demographic factors such as age, race/ethnicity, and gender. Regarding age, cases can be divided into groups based on when the disease, behavior, or exposure of interest is most likely to occur. For example, for vaccine-preventable diseases age groups are defined based on disease incidence, while for injuries, they can be determined according to the ages in which behaviors leading to specific types of injury are mostly likely to occur (e.g., school-aged children for bicycle accidents; adults for car accidents). For occupational exposures to toxicants, age groups could be defined in a way which allows us to understand how duration of exposure among older versus younger workers influences occurrence of disease in the former group. Age ranges should be narrow, i.e., cover only one or a few years, when disease incidence, or occurrence of the behavior or exposure is high, and broad where these factors are low.