n Learning and Teaching Mathematics - Calculating quartiles for box-and-whisker plots

Volume 2015, Issue 19
  • ISSN : 1990-6811


Quartiles are useful for describing the distribution of a data set as they split the distribution into four equal parts, each part containing one quarter of the total. As such, quartiles form a critical component of the "five-number summary" used for drawing box-and-whisker plots. Calculating the upper and lower quartiles of a data set should be a relatively straightforward procedure. However, while the basic concept of a quartile is simple enough, there are many different accepted methods for their calculation, with different methods producing slightly different numerical values. In this article I explore those particular methods that I have seen employed at school level in South Africa.

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