11.3 The following data relate to car production in the UK (not seasonally adjusted). 2003 2004 2005 2006 2007 January – 141.3 136 119.1 124.2 February – 141.1 143.5 131.2 115.6 March – 163 153.3 159 138 April – 129.6 139.8 118.6 120.4 May – 143.1 132 132.3 127.4 June – 155.5 144.3 139.3 137.5 July 146.3 140.5 130.2 117.8 129.7 August 91.4 83.2 97.1 73 – September 153.5 155.3 149.9 122.3 – October 153.4 135.1 124.8 116.1 – November 142.9 149.3 149.7 128.6 – December 112.4 109.7 95.3 84.8 –

(a) Graph the data for 2004–2006 by overlapping the three years (as was done in Figure 11.2) and comment upon any seasonal pattern.

(b) Use a 12-month moving average to find the trend values for 2004–2006.

(c) Find the monthly seasonal factors (multiplicative method). Describe the seasonal pattern that emerges.

(d) By how much is the August production figure below the July figure in general?

(e) Obtain the seasonally adjusted series. Compare it with the original series and comment.

(f) Compare the seasonal pattern found with that for consumers’ expenditure in Problem 11.1.