Third quartile

Definition

The third quartile (Q3) is the median of the upper half of a data set, representing the 75th percentile. It separates the highest 25% of data from the lowest 75%.

5 Must Know Facts For Your Next Test

1. Q3 is also known as the upper quartile.
2. To find Q3 in an ordered data set, first determine the median, then find the median of the upper half.
3. Q3 can be used to identify outliers in conjunction with Q1 and the interquartile range (IQR).
4. In a box plot, Q3 is represented by the top edge of the box.
5. The position of Q3 in a sorted data list can be calculated using $\frac{3(n + 1)}{4}$, where n is the number of observations.

Review Questions

• What does the third quartile (Q3) represent in a data set?
• How do you calculate Q3 for an ordered data set?
• What role does Q3 play in identifying outliers?

Related terms

First Quartile (Q1): The first quartile (Q1) is the median of the lower half of a data set, representing the 25th percentile.

Interquartile Range (IQR):

The interquartile range (IQR) is a measure of statistical dispersion, calculated as Q3 minus Q1.

Median:

The median is the middle value that separates a data set into two equal halves.