Editing Interquartile range (section)

===Data set in a plain-text box plot===
<pre style="font-family:monospace">
                             +−−−−−+−+
               * |−−−−−−−−−−−|     | |−−−−−−−−−−−|
                             +−−−−−+−+

 +−−−+−−−+−−−+−−−+−−−+−−−+−−−+−−−+−−−+−−−+−−−+−−−+   Number line
 0   1   2   3   4   5   6   7   8   9   10  11  12
</pre>

For the data set in this [[box plot]]:
* Lower (first) quartile ''Q''<sub>1</sub> = 7
* Median (second quartile) ''Q''<sub>2</sub> = 8.5
* Upper (third) quartile ''Q''<sub>3</sub> = 9
* Interquartile range, IQR = ''Q''<sub>3</sub> - ''Q''<sub>1</sub> = 2
* Lower 1.5*IQR whisker = ''Q''<sub>1</sub> - 1.5 * IQR = 7 - 3 = 4. (If there is no data point at 4, then the lowest point greater than 4.)
* Upper 1.5*IQR whisker = ''Q''<sub>3</sub> + 1.5 * IQR = 9 + 3 = 12. (If there is no data point at 12, then the highest point less than 12.)
* Pattern of latter two bullet points: If there are no data points at the true quartiles, use data points slightly "inland" (closer to the median) from the actual quartiles. 
This means the 1.5*IQR whiskers can be uneven in lengths. The median, minimum, maximum, and the first and third quartile constitute the [[Five-number summary]].<ref>Dekking, Kraaikamp, Lopuhaä & Meester, pp. 235–237</ref>