Quartiles

Definition

Quartiles divide a ranked data set into four equal parts. They are commonly used to understand the spread and center of the data.

5 Must Know Facts For Your Next Test

1. The first quartile (Q1) is the median of the lower half of the data set, not including the median if there is an odd number of observations.
2. The second quartile (Q2) is also known as the median of the entire data set.
3. The third quartile (Q3) is the median of the upper half of the data set.
4. Interquartile Range (IQR) is calculated as Q3 minus Q1 and measures the spread of the middle 50% of the data.
5. Outliers can be identified using quartiles by calculating $1.5 \times IQR$ above Q3 or below Q1.

Review Questions

Related terms

Median:

The value that separates a data set into two equal halves; it is also known as Q2 or the second quartile.

Percentiles:

Values that divide a data set into 100 equal parts, often used to provide more detailed information about distribution than quartiles.

Box Plot:

A graphical representation of a data set that shows its minimum, maximum, and three quartiles (Q1, Q2, Q3).