PERCENTILE

Contents

Definition

Relation between percentile, decile and quartile

Examples

See also

References

External links

Definition

A percentile is the value of a variable below which a certain percent of observations fall. So the 20th percentile is the value (or score) below which 20 percent of the observations may be found. The term percentile and the related term percentile rank are often used in descriptive statistics as well as in the reporting of scores from norm-referenced tests.
The 25th percentile is also known as the first quartile; the 50th percentile as the median.
One definition is that the pth percentile of n ordered values is obtained by first calculating the rank , rounded to the nearest integer and then taking the value that corresponds to that rank.^[1] One alternative method, used in many applications, is to use a linear interpolation between the two nearest ranks instead of rounding.
Linked with the percentile function, there is also a weighted percentile, where the percentage in the total weight is counted instead of the total number. In most spreadsheet applications there is no standard function for a weighted percentile.

Relation between percentile, decile and quartile

★ P₂₅ = Q₁

★ P₅₀ = D₅ = Q₂ = median value

★ P₇₅ = Q₃

★ P₁₀₀ = D₁₀ = Q₄

★ P₁₀ = D₁

★ P₂₀ = D₂

★ P₃₀ = D₃

★ P₄₀ = D₄

★ P₆₀ = D₆

★ P₇₀ = D₇

★ P₈₀ = D₈

★ P₉₀ = D₉
'Note:' One quartile is equivalent to 25 percentile while 1 decile is equal to 10 percentile.

Examples

When ISPs bill "Burstable" Internet bandwidth, the 95th or 98th percentile usually cuts off the top 5% or 2% of bandwidth peaks in each month, and then bills at the nearest rate. In this way infrequent peaks are ignored, and the customer is charged in a fairer way.
Physicians will often use infant and children's weight and height percentile as a gauge of relative health.

See also

★ Quantile

★ Quartile

★ Decile

★ Summary statistics

★ Percentile rank

References

http://www.itl.nist.gov/div898/handbook/prc/section2/prc252.htm
1. Statistical flaws in Excel

External links

★ Free Online Software (Calculator) computes Percentiles for any dataset according to 8 different percentile definitions.