A
percentage point (
pp) is the
unit for the
arithmetic difference of two
percentages. For example, going from 40% to 44% is a 4 percentage point increase. In the literature, the percentage point unit is usually either written out, or abbreviated as
pp,
p.p. or
%. Consider the following hypothetical example: In 1980, 40 percent of the population smoked, and in 1990 only 30 percent smoked. One can thus say that from 1980 to 1990, the prevalence of smoking decreased by 10
percentage points although smoking did not decrease by 10 percent (actually it decreased by
25 percent) – percentages indicate ratios, not differences.