The mid - points of class intervals xi along with respective frequencies fi for recorded observations are given. Calculate the mean deviations about mean ¯¯¯x
While calculating the mean of continuous frequency distributions we make assumption that frequency in each class is centered at its midpoint.
In a continuous frequency distribution once the mid points of class intervals are calculated the rest is same as for a discrete frequency distribution.
Total number of observation,N=∑ni=1fi.
∴¯x=∑ni=1fixiN
∴ Mean deviation about mean =∑ni=1fi|xi−¯x|N.