Question

8. What does empirical relation exist between quartile deviation, mean

deviation and standard deviation? If the quartile deviation of a series

is 60, the mean deviation of the series is​

Answer 1

For a Normal distribution with standard deviation sigma , mean deviation is given by [√(2/π)]sigma which is approximately equal to (4/5)*sigma.

Thus the statement mean deviation equal to 4/5 times the standard deviation is true only under the assumption of normality. Its not necessarily always true.