Page 1 - lesson notes 60 xi MOD m.d & s.d
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SAI INTERNATIONAL SCHOOL


                                                   ECONOMICS



                                                        Class-XI


                                  [STATISTICS FOR ECONOMICS]


                                                   CHAPTER -10


                                      MEASURES OF DISPERSION


                                                       Module-60



               TOPIC



                   •  Mean deviation( M.D) Grouped series
                   •   Standard deviation (S. D /  )Individual series (all


                       methods)

                   SHORT NOTES


                   Mean deviation is the arithmetic average of deviation of all the values taken

                   from a statistical average of series. In taking deviation of values, algebraic signs
                   + and – are not taken into consideration, that is negative deviations are also
                   treated as positive deviations .



               The formula for calculating mean deviation is


               M.D. = Σf|D|/N; where M.D. = Mean Deviation


               f is frequency of corresponding interval, N is total no. of frequencies
               (Σf)


               I DI read as Mod D = (X-A) is the modulus value or absolute value i.e.,

               deviations from median or mean or mode ignoring ± signs.
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