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Question
Obtain the trend line for the above data using 5 yearly moving averages.
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Solution
Construct the following table to obtain 5 yearly moving averages in data of problem 1.
| Year T | Production yt (in' 000 tonnes) |
5 – yearly moving total | 5 – yearly moving averages trend value |
| 1962 | 0 | – | – |
| 1963 | 0 | – | – |
| 1964 | 1 | 6 | 1.2 |
| 1965 | 1 | 8 | 1.6 |
| 1966 | 4 | 12 | 2.4 |
| 1967 | 2 | 20 | 4 |
| 1968 | 4 | 26 | 5.2 |
| 1969 | 9 | 32 | 6.4 |
| 1970 | 7 | 38 | 7.6 |
| 1971 | 10 | – | – |
| 1972 | 8 | – | – |
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| 1985 | 7 | – 2 | 4 | – 14 |
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| 2008 | 21 | 1 | -4 | 16 | -84 |
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| `sumx_t=68` | - | `sumu=0` | `sumu^2=60` | `square` |
The equation of trend is xt =a'+ b'u.
The normal equations are,
`sumx_t=na^'+b^'sumu ...(1)`
`sumux_t=a^'sumu+b^'sumu^2 ...(2)`
Here, n = 9, `sumx_t=68,sumu=0,sumu^2=60,sumux_t=-44`
Putting these values in normal equations, we get
68 = 9a' + b'(0) ...(3)
∴ a' = `square`
-44 = a'(0) + b'(60) ...(4)
∴ b' = `square`
The equation of trend line is given by
xt = `square`
