GCSE Maths (Edexcel)

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Interquartile Range

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Statistics Statistics

Interquartile Range

5:03 Quartiles
Spec S4
Previous Quartiles Next Analysing Cumulative Frequency Graphs
  • The interquartile range is a measure of spread in a data set
  • It is calculated by finding the difference between the upper quartile and the lower quartile
  • The lower quartile is the data value a quarter of the way into the data set, while the upper quartile is three quarters of the way in
  • The interquartile range focuses on the middle half of the data, ignoring the extreme values
  • It is often more accurate than the range in measuring spread, as it is not affected by outliers as much
  • To calculate the interquartile range, the data values must be in order
  • The position of the lower quartile is (number of data values + 1) / 4
  • The position of the upper quartile is 3 * (number of data values + 1) / 4
  • The interquartile range is the difference between the values in the lower and upper quartiles

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