Forum Discussion
Excel Box and Whiskers
In this example, 32 is an outlier because it is less than 1.5 times the interquartile range below the lower quartile:
= Q1 - 1.5 * (Q3 - Q1)
= 37 - 1.5 * (40 - 37)
= 37 - 1.5 * 3
= 37 - 4.5
= 32.5
Thus, any value lower than 32.5 in this data set is an outlier. Therefore, 32 is an outlier. Since 32 is an outlier, it is plotted outside of the whiskers (i.e. a single dot). The next lowest value that is not an outlier becomes the lower whisker. Since 37 is both Q1 AND the lowest non-outlier in the data set, it becomes the "whisker". Because of this, the whisker is plotted on 37. In this case, you do not have a visual lower whisker. In summation, excel has plotted this data set correctly.
Hello PReagan,
Thanks for your explanation.
But it doesn't solve my problems.
I always need 2 whiskers, not sometimes a oulier / point.
How can I get two whiskers for every situation?
Greetings
Erwin
Can I ask the purpose of always having two whiskers? That might help me understand your problem a little better.
Just to reiterate, the way that a box and whisker plot is intended to be used is such that outliers are plotted beyond Q1 - 1.5*IQR and Q3 + 1.5*IQR. Is this not what you intend to do?Hello PReagan,
We don't know the rule Q1 - 1.5*IQR and Q3 + 1.5*IQR you metionned to decide if we would / should draw an outliner instead of a whisker.
We work always with the values minimum, Q1, Q2, Q3 and the maximum value and then we draw the boxplot that is the box (between Q1 - Q3) with the two whiskers included (from min tot Q1 and from Q3 to max).
You can see how we work in the youtube film https://www.youtube.com/watch?reload=9&v=37-1ILIBCOA (sorry that is is in dutch)
It is possible that a whisker diappear but this is only in the case that the minimum value is equal to Q1 (then the lower whisker is gone) or when Q3 is equal to the maximum value (then the higher whisker is gone).
We don't know (and don't use) the rule Q1 - 1.5*IQR and Q3 + 1.5*IQR. to decide if we would draw a whisker or an outliner. We don't know the term outliner. We even don't know the mechanism you mentionned.
Recapitulating, We allways draw a box and two whiskers (except when min value = Q1 or Q3 = maximum value).
So I was very supprised to see sometimes a whisker disappearing / appearing in excel, .... I didn't understand why.
I hope you now understand my problem. I never need an outliner, but always a lower whisker (when minimum value is different from Q1), then a box between the values Q1 - Q2 - Q3 and then the Higer whisker (when Q3 is different from the maximum value)
Greetings
Erwin
- You can see at http://www.hhofstede.nl/modules/boxplot.htm that we always have a boxplot and two whiskers even if there is a big difference between the minimum value and q1 and when there is a big difference between Q3 and the maximum value.