Explain find the seasonal index and trend line and forecast it.
Quarterly billing for water usage is shown below-
|
|
Year
|
|
Quarter
|
1
|
2
|
3
|
4
|
|
|
Winter
|
64
|
66
|
68
|
73
|
|
|
Spring
|
103
|
103
|
104
|
120
|
|
|
Summer
|
152
|
160
|
162
|
176
|
|
|
Fall
|
73
|
72
|
78
|
88
|
|
1) Find the seasonal index for each quarter.
2) Depersonalize the data.
3) Find the trend line.
4) Presume there is no cyclical component (don't forget- there IS a seasonal component). Forecast the summer billing for year 5.