to avoid confusion with percentage increase or decrease in the actual quantity.
One can thus say that from 1980 to 1990, the prevalence of smoking decreased by 10 percentage points (or by 10 percent of the population) or by 20 percent when talking about smokers only – percentages indicate proportionate part of a total.
The drug reduces absolute risk by 20 percentage points.
Alternatives may be more meaningful to consumers of statistics, such as the reciprocal, also known as the number needed to treat (NNT).
For measurements involving percentages as a unit, such as, growth, yield, or ejection fraction, statistical deviations and related descriptive statistics, including the standard deviation and root-mean-square error, the result should be expressed in units of percentage points instead of percentage.