Our Methods

The County Health Rankings, a program of the University of Wisconsin Population Health Institute, measures the health of nearly all counties in the nation and ranks them within states. The Rankings are compiled using county-level measures from a variety of national and state data sources. These measures are standardized and combined using scientifically-informed weights. To learn more about research on our methods, see our selected publications.

Rankings overview

We suggest starting with the County Health Rankings model. It provides the foundation for the entire ranking process. ​Counties in each of the 50 states are ranked according to summaries of a variety of health measures. Those ranking in the healthiest 75-100% of counties are considered to be the “healthiest.” Counties are ranked relative to the health of other counties in the same state.

Learn more about the ranking system.

How CHR&R measures are selected

The County Health Rankings team uses a careful and deliberate process when selecting which measures will be included. We look for data that reflect meaningful aspects of population health and equity; build awareness of the multiple factors that influence health; support leaders in growing community power to improve health equity; and are technically and methodologically strong and feasible. We select our measures carefully so that people can use our data to set agendas, plan their program activities, educate their communities and allocate their resources.

Learn more about how we select our measures. 

Data quality

The County Health Rankings team draws upon the most reliable and valid measures available to compile the Rankings. Where possible, we provide the margins of error (95% confidence intervals) for our measure values. In many cases, the values of specific measures in different counties are not statistically different from one another; however, when combined using our model, those various measures produce different rankings.

Learn more about our data quality.

What's a county?

The County Health Rankings are based on counties and county equivalents (ranked places). Any entity that has its own Federal Information Processing Standard (FIPS) county code is included in the Rankings. We only rank counties and county equivalents within a state. The major goal of the Rankings is to raise awareness about the many factors that influence health and that health varies from place to place, not to produce a list of the healthiest 10 or 20 counties in the nation and only focus on that. 

Learn more about what we rank.

Calculating quartiles and county ranks

The County Health Rankings are compiled from many different types of data. To calculate the ranks, we first standardize each of the measures using a z-score. The ranks are then calculated based on weighted sums of the standardized measures within each state. The county with the lowest z-score (best health) gets a rank of #1 for that state and the county with the highest score (worst health) is assigned a rank corresponding to the number of places we rank in that state. Counties are then grouped into four equally sized groups (quartiles) from Least Healthy to Healthiest (Lowest 0-25%, Lower 25-50%, Higher 50-75%, and Healthiest 75-100%) within each state. The county with a rank of #1 can be found in the Healthiest (Healthiest 75-100%) quartile. 

Learn more about how we calculate ranks.