Sheppard's correction

Sheppard's correction

[′shep·ərdz kə‚rek·shənz]
(statistics)
A correction for moments computed for a frequency distribution of grouped data to adjust for the error that is introduced by the assumption that all the data within a class are at the midpoint of the class; the adjustment is made by subtracting one-twelfth of the square of a grouping unit from the estimated variance.