Interquartile Range


  • Interquartile range (IQR) is the measure of dispersion or spread of data. It is also known as Midspread or H-Spread. 
  • The IQR is a measure of variability, based on dividing a data set into quartiles.
  • First you understand what is quartile? Please visit Quartile section for more understanding. In brief, Quartile is the division of data into four equal parts. Data points are Q1, Q2 and Q3.

                        


The distance between first and third quantiles is Interquartile range (IQR).

IQR = Q3 - Q1

IQR is used to plot the box plots and finding the outliers.

Thumb rule to identify suspected outlier is to single out values falling at least 1.5 x IQR above the third or below the first quartile.

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