Written by the Fiveable Content Team • Last updated August 2025
Written by the Fiveable Content Team • Last updated August 2025
Definition
Percentiles are values that divide a data set into 100 equal parts, indicating the relative standing of an observation within the data. They are commonly used to understand and interpret the distribution of data points.
AP course connection
Topic 2.3: 2.3 Measures of the Location of the Data
The 50th percentile is known as the median, which divides the data set into two equal halves.
To find a specific percentile, you first need to arrange the data in ascending order.
The formula for finding the rank of a percentile is $P_k = \frac{k}{100} \cdot (N+1)$, where $k$ is the desired percentile and $N$ is the number of observations.
Percentiles can be used to identify outliers by examining values at extreme percentiles such as the 1st or 99th percentiles.
In a normal distribution, approximately 68% of data falls between the 16th and 84th percentiles.
Related terms
Quartiles: Values that divide a data set into four equal parts. The first quartile (Q1) represents the 25th percentile, and so on.