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##### Wiktionary
percentage point

n. One hundredth of a given value, used to measure the difference of two percentages.

##### WordNet
percentage point

n. the dot at the left of a decimal fraction [syn: decimal point]

##### Wikipedia
Percentage point

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.

Percentage point differences are one way to express a risk or probability. Consider a drug that cures a given disease in 70 percent of all cases, while without the drug, the disease heals spontaneously in only 50 percent of cases. 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). In this case, the reciprocal transform of the percentage point difference would be 1/(20%) = 1/0.20 = 5. Thus if 5 patients are treated with the drug, one could expect to heal one more case of the disease than would have occurred in the absence of the drug.

For measurements with percentage as unit, like growth, yield, or ejection fraction, the standard deviation will have percentage points as unit. Mistakenly using percentage as the unit for the standard deviation is confusing since percentage is also used as a unit for the relative standard deviation, i.e. the standard deviation divided by the average value ( Coefficient of Variation).

#### Usage examples of "percentage point".

Not even a cat's whisker of difference, but people like this, as competitive as any athletes could ever be, worked damned hard for that fifth of a percentage point, and it really came down to who'd had what for breakfast on the mornings of the competitive exercises, or maybe what they'd dreamed about doing the night.

But those who anticipate the successful negotiation of a formal peace treaty with Haven have dropped another half percentage point.

This election is going to be decided by a percentage point or two.

But Clemenza felt strongly that it was important to keep good working habits and never give away a fraction of a percentage point.

Moreover, studies have shown that an unemployment decline of 1 percentage point accounts for a 1 percent drop in nonviolent crime.

The circumstances of his wife's death were well-known, and had probably added a percentage point of sympathy votes in the last election.

The difference between Ender and Bean amounted to half of a percentage point.

The shift of a percentage point or two in the approval rating for a product can cause us to retool a factory or to scrap a line altogether.

Dana had to get his calculations to agree to within a ten-thousandth of a percentage point: the goal, in fact, was to get five balls, a perfect reading of .