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Box Plot Q3 Calculation

Go to solution Solved by Andrew Berridge,

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When working with a box plot or violin chart. The Q3 result is different to what I get in excel and chat gpt.
Using simple values as an example. 3 , 4 , 5 , 5 , 7, 8 , 9 , 10 , 11 , 11, 12.
Q3 in excel = 11 
Spotfire = 10.5 

from chat gpt

  1. Median (Q2):

    • The dataset has an odd number of values, so the median is the middle value.
    • Median (Q2) = 8 (the 6th value in the sorted dataset)
  2. First Quartile (Q1):

    • Counting from the start, Q1 is the median of the first half of the dataset.
    • Q1 = median of (3, 4, 5, 5, 7) = 5 (the 3rd value in the sorted dataset)
  3. Third Quartile (Q3):

    • Counting from the end, Q3 is the median of the second half of the dataset.
    • Q3 = median of (9, 10, 11, 11, 12) = 11 (the 4th value in the sorted dataset)

So, for the given dataset, the median (Q2) is 8, the first quartile (Q1) is 5, and the third quartile (Q3) is 11.



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  • Solution

Hi Brian,

Great question!

As it happens, there are many different methods to calculate the quartiles.

Take a look at this Wikipedia page. There are at least 4 standard methods for calculating them:


R can use one of 9 different methods...

Spotfire, and the Violin Mod use the type 7 method here:


This is the default for R, and if it's good enough for R, I would say it's good enough for Spotfire.

However, if you absolutely NEED it to match Excel, then I could consider implementing the Excel-type calculations for the Violin Mod, as an option.

Let me know in a reply!


Andrew (Violin Mod author, Spotfire Field Tech Team)



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Hello Andrew 

Thank you for the reply and for the link to the explanation. 

Thanks for the offer to alter the mod to match excel, however now that I have an understanding of how it is calculated it is all good as I will be able to explain it in the visualization.


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