Quartile Deviation – Statistics

The points that divide the distribution in to four equal parts are called quartiles. If we take the difference between the third quartile and the first quartile, it gives us a value called inter quartile range. It is equal to

  • Q3 – Q1. Half of this is the Semi-Inter Quartile Range or quartile deviation which is (Q3 – Q1)/2 .
  • Quartile deviation is also called the semi-inter quartile range.

Formula to find the quartile deviations:

First quartile(Q1) = n+1/4 th score

Median(Q2) = n+1/2 th score

Third quartile(Q3) = 3(n+1)/4 th score

Quartile deviation = Q3 Q1/2 th score

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