A quartile is a specialized quantile. It divides the data into 4 approximately equal groups.
The first and third quartile (or the 25th and 75th percentiles) are two very commonly used percentiles. Because they divide the data into quarters (when taken together with the median), they are referred to as the lower and upper quartiles. They are sometimes abbreviated Q_1 and Q_3.
Technically, the median is a “middle” quartile and is sometimes referred to as Q_2. Some also refer to the minimum value in a data set as Q_0 and the maximum as Q_4.
| Quartile Abbreviations | Description | Percentile |
|---|---|---|
| Q_0 | Minimum Value | 0th percentile |
| Q_1 | Lower quartile | 25th percentile |
| Q_2 | Middle quartile (median) | 50th percentile |
| Q_3 | Upper quartile | 75th percentile |
| Q_4 | Maximum Value | 100th percentile |