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Unit 8: Descriptive Statistics




          The highest frequency total in each of the six columns is identified and analysed to determine  Notes
          mode. We apply this method for determining mode of the above example.


                             X    f (1)  (2)   (3)     (4)   (5)  (6)
                             10    8
                                         23
                             11   15                   43
                                               35
                                                             135
                             12   20
                                         120
                             13   100                             218
                                               198
                             14   98                   293
                                         193
                             15   95                         283
                                               185
                             16   90                              260
                                         165
                                                       215
                             17   75
                                               125
                             18   50                         155
                                         80
                             19   30
                                          Analysis  Table
                 V        A     R     I      A     B     L      E
               Columns   10     11    12    13     14    15    16     17    18    19
                 1                           1
                 2                                 1     1
                 3                           1     1
                 4                           1     1     1
                 5                                 1     1      1
                 6                                       1      1     1
                Total     0     0     0      3     4     4      2     1     0      0
          Since the value 14 and 15 are both repeated maximum number of times in the analysis table,
          therefore, mode is ill defined. Mode in this case can be approximately located by the use of the
          following formula, which will be discussed later, in this unit.
                                     Mode = 3 Median – 2 Mean
                                   Calculation of  Median  and  Mean

            X      10   11    12    13    14     15    16     17    18    19    Total
            f      8    15    20    100   98     95    90     75    50    30    581

            C.f.   8    23    43    143   241    336   426    501   551   581
            fX     80   165   240   1300   1372   1425   1440   1275   900   570   8767

                            +
                        æ  581 1ö                               8767
          Median = Size of  ç è  2  ÷ ø th,  i.e., 291st observation = 15. Mean =   581  =  15.09
                Mode = 3 × 15 – 2 × 15.09 = 45 – 30.18 = 14.82




             Notes  If the most repeated values, in the above analysis  table, were  not adjacent,  the
             distribution would have been bimodal, i.e., having two modes





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