It is affected by sampling fluctuations 75 mean

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Unformatted text preview: es computed from any measure of central tendency; i.e., the mean, median or mode, all the deviations are taken as positive i.e., signs are ignored. According to Clark and Schekade, “Average deviation is the average amount scatter of the items in a distribution from either the mean or the median, ignoring the signs of the deviations”. We usually compute mean deviation about any one of the three averages mean, median or mode. Some times mode may be ill defined and as such mean deviation is computed from mean and median. Median is preferred as a choice between mean and median. But in general practice and due to wide applications of mean, the mean deviation is generally computed from mean. M.D can be used to denote mean deviation. 7.5.2 Coefficient of mean deviation: Mean deviation calculated by any measure of central tendency is an absolute measure. For the purpose of comparing variation among different series, a relative mean deviation is required. The relative mean deviation is obtained by dividing the mean deviation by the average used for calculating mean deviation. 149 Mean deviation Mean or Median or Mode If the result is desired in percentage, the coefficient of mean Mean deviation deviation = × 100 Mean or Median or Mode 7.5.3 Computation of mean deviation – Individual Series : 1. Calculate the average mean, median or mode of the series. 2. Take the deviations of items from average ignoring signs and denote these deviations by |D|. 3. Compute the total of these deviations, i.e., Σ |D| 4. Divide this total obtained by the number of items. ∑ |D| Symbolically: M.D. = n Example 6: Calculate mean deviation from mean and median for the following data: 100,150,200,250,360,490,500,600,671 also calculate coefficients of M.D. Coefficient of mean deviation: = Solution: Mean = x = ∑x n = 3321 =369 9 Now arrange the data in ascending order 100, 150, 200, 250, 360, 490, 500, 600, 671 n + 1 Median = Value of item 2 th 9 + 1 = Value of item 2 = Value of 5th item = 360 th 150 X D = x...
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