**Quartiles** are the values that break down the dataset into **quarters**, or **quartiles**:

- The first quartile (
**Q1**) is the point below which a **quarter** of the data lies. It is sometimes called the **lower quartile**.
- The second quartile (
**Q2**) is the point **below** which **half** of the data lies. We already know this point by the name of median. It is also called the **middle quartile**.
- The third quartile (
**Q3**) is the point below which **three-quarters** of the data lies. It is called the **upper quartile**.

Let's calculate quartiles for the following set:

1, 2, 3, 4, 5, 6, 7, 8, 9, 10

We already know how to calculate median (the **middle quartile**). In this case, the middle quartile is **5.5**. Below this point, we have half the data `\{1, 2, 3, 4, 5\}`

, and above this point, we have the other half, `\{6, 7, 8, 9, 10\}`

. The median for the lower half of the data is **3**; below this point, we have one-quarter of all the data, or half of the data for that subset. Thus, **3** is the **lower quartile**.

Let's now consider the second half of the set. The median of this set is **8**, and this is also the upper quartile of the whole set.