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%.
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Q3 is also known as the upper quartile.
To find Q3 in an ordered data set, first determine the median, then find the median of the upper half.
Q3 can be used to identify outliers in conjunction with Q1 and the interquartile range (IQR).
In a box plot, Q3 is represented by the top edge of the box.
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.
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Related terms
First Quartile (Q1): The first quartile (Q1) is the median of the lower half of a data set, representing the 25th percentile.