Percentiles

The percentile (this term was first used by Galton, 1885a) of a distribution of values is a number xp such that a percentage p of the population values are less than or equal to xp. For example, the 25th percentile (also referred to as the .25 quantile or lower quartile) of a variable is a value (xp) such that 25% (p) of the values of the variable fall below that value.

Similarly, the 75th percentile (also referred to as the .75 quantile or upper quartile) is a value such that 75% of the values of the variable fall below that value and is calculated accordingly. You can specify the method of computing percentiles in the Options dialog box - Analyses/Graphs: Limits tab. For more information, see Percentile Calculation Options in STATISTICA. User-specified percentiles can be calculated in Nonparametrics.