Percentiles

Definition

Percentiles are measures that divide a dataset into 100 equal parts, indicating the relative standing of a value within the data. For example, the 25th percentile (first quartile) is the value below which 25% of the observations fall.

5 Must Know Facts For Your Next Test

1. The median is the 50th percentile, dividing data into two equal halves.
2. Percentiles are useful for comparing scores across different datasets or distributions.
3. Common percentiles include quartiles (25th, 50th, and 75th percentiles).
4. To find a specific percentile, data must be ordered from smallest to largest.
5. Percentiles can be used to identify outliers by examining values at extreme percentiles (e.g., below the 5th or above the 95th).

Review Questions

• What does the median represent in terms of percentiles?
• How do you interpret the value of the 75th percentile in a dataset?
• Why are percentiles important in statistical analysis?

Related terms

Quartile: A type of percentile that divides data into four equal parts; includes Q1 (25th percentile), Q2 (50th percentile), and Q3 (75th percentile).

Interquartile Range (IQR): $IQR = Q3 - Q1$; measures statistical dispersion and helps identify outliers.

Median: $Q2$ or $50^{\text{th}}$ percentile; it represents the middle value when data is ordered.