Formula
1. Mean deviation of mean `delta bar x = (sum f*|x - bar x|)/n`
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2. Mean deviation of median `delta M = (sum f*|x - M|)/n`
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3. Mean deviation of mode `delta Z = (sum f*|x - Z|)/n`
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Examples
1. Calculate Mean deviation about mean from the following grouped data
Class-X | Frequency |
2 - 4 | 3 |
4 - 6 | 4 |
6 - 8 | 2 |
8 - 10 | 1 |
Solution:
Mean `bar x=(sum f x)/(sum f)`
`=52/10`
`=5.2`
Class `(1)` | `f` `(2)` | Mid value (`x`) `(3)` | `f*x` `(4)=(2)xx(3)` | `|x-bar x|=|x-5.2|` `(5)` | `f*|x-bar x|` `(6)=(2)xx(5)` |
2 - 4 | 3 | 3 `3=(2+4)/2` | 9 `9=3xx3` `(4)=(2)xx(3)` | 2.2 `|3-5.2|=2.2` `|x - 5.2|` | 6.6 `6.6=3xx2.2` `(6)=(2)xx(5)` |
4 - 6 | 4 | 5 `5=(4+6)/2` | 20 `20=4xx5` `(4)=(2)xx(3)` | 0.2 `|5-5.2|=0.2` `|x - 5.2|` | 0.8 `0.8=4xx0.2` `(6)=(2)xx(5)` |
6 - 8 | 2 | 7 `7=(6+8)/2` | 14 `14=2xx7` `(4)=(2)xx(3)` | 1.8 `|7-5.2|=1.8` `|x - 5.2|` | 3.6 `3.6=2xx1.8` `(6)=(2)xx(5)` |
8 - 10 | 1 | 9 `9=(8+10)/2` | 9 `9=1xx9` `(4)=(2)xx(3)` | 3.8 `|9-5.2|=3.8` `|x - 5.2|` | 3.8 `3.8=1xx3.8` `(6)=(2)xx(5)` |
--- | --- | --- | --- | --- | --- |
-- | `n=10` | -- | `sum f*x=52` | -- | `sum f*|x-bar x|=14.8` |
Mean deviation of Mean
`delta bar x = (sum f*|x - bar x|)/n`
`delta bar x = 14.8/10`
`delta bar x = 1.48`
Coefficient of Mean deviation `=(delta bar x)/(bar x)`
`=1.48/5.2`
`=0.28`
2. Calculate Mean deviation about mean from the following grouped data
Class-X | Frequency |
10 - 20 | 15 |
20 - 30 | 25 |
30 - 40 | 20 |
40 - 50 | 12 |
50 - 60 | 8 |
60 - 70 | 5 |
70 - 80 | 3 |
Solution:
Mean `bar x=(sum f x)/(sum f)`
`=3080/88`
`=35`
Class `(1)` | `f` `(2)` | Mid value (`x`) `(3)` | `f*x` `(4)=(2)xx(3)` | `|x-bar x|=|x-35|` `(5)` | `f*|x-bar x|` `(6)=(2)xx(5)` |
10 - 20 | 15 | 15 | 225 | 20 | 300 |
20 - 30 | 25 | 25 | 625 | 10 | 250 |
30 - 40 | 20 | 35 | 700 | 0 | 0 |
40 - 50 | 12 | 45 | 540 | 10 | 120 |
50 - 60 | 8 | 55 | 440 | 20 | 160 |
60 - 70 | 5 | 65 | 325 | 30 | 150 |
70 - 80 | 3 | 75 | 225 | 40 | 120 |
--- | --- | --- | --- | --- | --- |
-- | `n=88` | -- | `sum f*x=3080` | -- | `sum f*|x-bar x|=1100` |
Mean deviation of Mean
`delta bar x = (sum f*|x - bar x|)/n`
`delta bar x = 1100/88`
`delta bar x = 12.5`
Coefficient of Mean deviation `=(delta bar x)/(bar x)`
`=12.5/35`
`=0.3571`
This material is intended as a summary. Use your textbook for detail explanation.
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