The **upper** **quartile** of a set of data is the median of the higher half of the data.

The **lower** **quartile** of a set of data is the median of the lower half of the data.

The **interquartile** **range** is the difference between the upper and lower quartiles and gives an indication of the statistical dispersion or spread of the given data.

**Example**

Find the interquartile range of the following set of data:

3 4 5 5 7 7 7 8 9 10

**Answer**

Divide the data into two halves.

3 4 5 5 7 7 7 8 9 10

The lower quartile is the median of the blue lower half.

3 4 5 5 7

The lower quartile is **5**.

The upper quartile is the median of the red higher half.

7 7 8 9 10

The upper quartile is 8.

The interquartile range is 8 - 5 = **3**.