In: Statistics and Probability
Refer to the gasoline sales time series data in the given table.
| Week | Sales (1000s of gallons) | 
| 1 | 18 | 
| 2 | 22 | 
| 3 | 18 | 
| 4 | 24 | 
| 5 | 19 | 
| 6 | 16 | 
| 7 | 21 | 
| 8 | 19 | 
| 9 | 22 | 
| 10 | 19 | 
| 11 | 16 | 
| 12 | 23 | 
Week  | 
Sales  | 
4-Week Moving Average  | 
5-Week Moving Average  | 
| 1 | 18 | ||
| 2 | 22 | ||
| 3 | 18 | ||
| 4 | 24 | ||
| 5 | 19 | ||
| 6 | 16 | ||
| 7 | 21 | ||
| 8 | 19 | ||
| 9 | 22 | ||
| 10 | 19 | ||
| 11 | 16 | ||
| 12 | 23 | 
a) Four Week moving average:
| Week | Sales | Four week moving Average | Error | Error² | |
| 1 | 18 | - | - | - | - | 
| 2 | 22 | - | - | - | - | 
| 3 | 18 | - | - | - | - | 
| 4 | 24 | - | - | - | - | 
| 5 | 19 | (18+22+18+24)/4 = | 20.500 | -1.500 | 2.250 | 
| 6 | 16 | (22+18+24+19)/4 = | 20.750 | -4.750 | 22.563 | 
| 7 | 21 | (18+24+19+16)/4 = | 19.250 | 1.750 | 3.063 | 
| 8 | 19 | (24+19+16+21)/4 = | 20.000 | -1.000 | 1.000 | 
| 9 | 22 | (19+16+21+19)/4 = | 18.750 | 3.250 | 10.563 | 
| 10 | 19 | (16+21+19+22)/4 = | 19.500 | -0.500 | 0.250 | 
| 11 | 16 | (21+19+22+19)/4 = | 20.250 | -4.250 | 18.063 | 
| 12 | 23 | (19+22+19+16)/4 = | 19.000 | 4.000 | 16.000 | 
| Total | -3.000 | 73.750 | |||
Five Week moving Average :
| Month | Sales | Five week moving Average | Error | Error² | |
| 1 | 18 | - | - | - | - | 
| 2 | 22 | - | - | - | - | 
| 3 | 18 | - | - | - | - | 
| 4 | 24 | - | - | - | - | 
| 5 | 19 | - | - | - | - | 
| 6 | 16 | (18+22+18+24+19)/5 = | 20.200 | -4.200 | 17.640 | 
| 7 | 21 | (22+18+24+19+16)/5 = | 19.800 | 1.200 | 1.440 | 
| 8 | 19 | (18+24+19+16+21)/5 = | 19.600 | -0.600 | 0.360 | 
| 9 | 22 | (24+19+16+21+19)/5 = | 19.800 | 2.200 | 4.840 | 
| 10 | 19 | (19+16+21+19+22)/5 = | 19.400 | -0.400 | 0.160 | 
| 11 | 16 | (16+21+19+22+19)/5 = | 19.400 | -3.400 | 11.560 | 
| 12 | 23 | (21+19+22+19+16)/5 = | 19.400 | 3.600 | 12.960 | 
| Total | -1.600 | 48.960 | |||
b)
MSE for four week moving average = ∑(A-F)²/n = 73.75/8 = 9.22
MSE for four week moving average = ∑(A-F)²/n = 48.96/7 = 6.99
c)
5 week moving average is the best.