Interquartile range

Definition

The interquartile range (IQR) measures the spread of the middle 50% of a data set. It is calculated as the difference between the third quartile (Q3) and the first quartile (Q1).

5 Must Know Facts For Your Next Test

1. IQR = Q3 - Q1.
2. The IQR is used to measure statistical dispersion.
3. It helps identify outliers; data points that fall below Q1 - 1.5*IQR or above Q3 + 1.5*IQR are considered outliers.
4. Unlike range, IQR is not affected by extreme values in the data set.
5. Quartiles divide data into four equal parts, with Q1 representing the 25th percentile and Q3 representing the 75th percentile.

Review Questions

• How do you calculate the interquartile range?
• Why is IQR preferred over range when measuring data spread?
• What role does IQR play in identifying outliers?

Related terms

Quartile: A type of quantile that divides a data set into four equal parts.

Median: The middle value of a data set when it is ordered from least to greatest.

Range: The difference between the maximum and minimum values in a data set.