The formula for calculating the position of the whiskers is

Q3+1.5IQR and Q1-1.5IQR

But doesn't that mean that the length of the whiskers should be of the same length? How are they of different lengths in some boxplots?


Not necessarily. The whiskers actually end at the highest point within $Q3+1.5R$ and at the lowest point above $Q1-1.5R$. So for instance if $Q3+1.5R=100$ and the highest value in your sample is $90$ then the whisker will end at $90$. You must be observing something like this.

  • $\begingroup$ Okay so the line at both whiskers end depending on the data points in our sample? $\endgroup$ Jun 18 '17 at 16:09
  • $\begingroup$ Yes but if there are points above Q3+1.5R then it will end at Q3+1.5R otherwise at the maximum value below that. That is why if there are points above Q3+1.5R and below Q1-1.5R then the length of the whiskers look the same. $\endgroup$ Jun 18 '17 at 16:20

Not the answer you're looking for? Browse other questions tagged or ask your own question.