Question: how to find the quartile deviation for grouped data?
Answer: Q D = Q 3 − Q 1 2. The inter-quartile range is given by I Q R = Q 3 − Q 1 . Q i = ( i ( N ) 4 ) t h value, where is the total number of observations. The cumulative frequency just greater than or equal to is . ...  The cumulative frequency just greater than or equal to is . ...  The quartile deviation ( ) is.