Hillstone SA manufactures and sells tyres to the passenger vehicle market in southern Africa. The quarterly sales (in 1 000s of units) are shown in the table below. The marketing department wishes to apply time series analysis to estimate future quarterly passenger vehicle tyre sales for 2012 and 2013.
|
Year
|
Quarter
|
Tyressold
|
|
2005
|
Jan-Mar
|
64 876
|
|
|
Apr-Jun
|
58 987
|
|
|
Jul-Sep
|
54 621
|
|
|
Oct-Dec
|
62 345
|
|
2006
|
Jan-Mar
|
68 746
|
|
|
Apr-Jun
|
66 573
|
|
|
Jul-Sep
|
60 927
|
|
|
Oct-Dec
|
71 234
|
|
2007
|
Jan-Mar
|
78 788
|
|
|
Apr-Jun
|
71 237
|
|
|
Jul-Sep
|
68 098
|
|
|
Oct-Dec
|
74 444
|
|
2008
|
Jan-Mar
|
77 659
|
|
|
Apr-Jun
|
76 452
|
|
|
Jul-Sep
|
73 456
|
|
|
Oct-Dec
|
78 908
|
|
2009
|
Jan-Mar
|
84 563
|
|
|
Apr-Jun
|
81 243
|
|
|
Jul-Sep
|
74 878
|
|
|
Oct-Dec
|
86 756
|
|
2010
|
Jan-Mar
|
91 556
|
|
|
Apr-Jun
|
85 058
|
|
|
Jul-Sep
|
77 035
|
|
|
Oct-Dec
|
80 145
|
|
2011
|
Jan-Mar
|
102 923
|
|
Apr-Jun
|
96 456
|
(a) Use Excel to develop a time series model that Hillstone can use to prepare seasonally adjusted trend forecasts of passenger vehicle tyre sales on a quarterly basis.
(b) Prepare seasonally adjusted trend forecast estimates for 2012 and 2013 on a quarterly basis.
(c) What confidence could the Hillstone management have in the estimates produced? Comment briefly.