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3.4 Annotation and Suppression of Unstable Rates

For rare injuries and/or for small populations, a rate might be based on a very small number of deaths. When the total number of deaths used to calculate any rate (crude, age-adjusted, or smoothed) is 20 or less, the rate is considered statistically unstable. States or counties with unstable rates are displayed using a cross-hatch pattern in maps.

In map headings and hover-over windows, and also in data downloads, any unstable rate will at a minimum be annotated as such, and in some instances will be suppressed entirely. Suppression variously depends on the geographic level of the map element (county, state, regional, or national) being referenced and the death count associated with the rate. The suppression rules are as follows:

• A county-level rate that is unstable (associated death count ≤ 20) will always be suppressed.
• A state-level rate that is unstable (associated death count ≤ 20) can be displayed (but annotated as unstable) provided that the death count ≥10 (per data privacy rules); otherwise the rate will be suppressed.
• A regional or national rate that is unstable (associated death count ≤ 20) can be displayed without restriction (but will be annotated as unstable).

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