Why Ranks Change
We encourage using changes in rank to start investigating what might be occurring in your county. Large changes in rank may indicate interesting changes in health. However, there are many reasons ranks could change. So, it should not be used as a metric to measure progress, but rather, another tool in your toolbox to assess the current health of your county.
In order to better understand why your county’s rank may have changed from the previous year, the best place to start is by examining the individual measures that comprise the rank. When examining each of these underlying components, it is helpful to explore the following:
- Your county’s measures over time: Are measure values increasing, decreasing, or staying the same? For instance, take a look at the trend graph for your county’s premature death estimate. Is premature death in your county increasing, decreasing, or staying the same? How does your county’s trend compare to the state or national trend? Looking more closely at changes over time in your county’s underlying measures can help you better understand your county’s progress and potential influence on the change in your rank.
- Error margins associated with your county’s estimates: Another thing to consider is the error associated with the measures comprising the rank. Year-to-year, even if your county’s true rate does not change, there will be some fluctuation in the measure due to random variation. For instance, it is possible to see substantial change in your county’s premature death rate from the previous year, but if the rate is within the margin of error for the previous year’s premature death rate, the change may be partially or almost completely due to random fluctuation in measures from year-to-year. Counties with smaller populations are particularly susceptible to this variation.
Ranks can improve or worsen for one or more reasons:
- Your county experienced health gains or losses: Change in a rank can be due to actual change in the underlying measures that comprise the summary rank.
- Other counties experienced health gains or losses: A rank may also improve or worsen not due to change in your own county’s measures, but rather because of changes in counties ranked just above or below your county within the state.
- Random variation in measures: Since all measures have some variation (which is why we report error margins), a fluctuation in county rank may be caused by random variation in the measures that comprise the rank.
- Changes in ranked measures or their methods: Ranks can be influenced by the introduction of new measures or a change in the methods for current measures. For instance, the 2019 Rankings were calculated using two new years of Premature Death data, which increases the potential for change in Health Outcomes ranks from the previous year. Additionally, underlying methodology changes or updates in the data source for the Mammography Screening and Preventable Hospitalizations, as well as the addition of the new Flu Vaccination measure may lead to more changes in these Clinical Care measures and thus Health Factors ranks.