Problem 5. Forecasting

It appears from the data for the Tesla Model S sales from the Inside EVs scorecard that sales follow a monthly adjustment (similar to a seasonal adjustment, but by month).

	Year	1	2	3	4
Month	2014	2015	2016	2017
1	January	800	1100	850	900
2	February	1089	1150	1550	1750
3	March	1300	2450	3990	3450
4	April	1100	1700	800	1125
5	May	1000	2400	1200	1620
6	June	1500	2800	3700	2250
7	July	800	1600	1954	1425
8	August	600	1300	2852	2150
9	September	2500	2500	4350	4860
10	October	1300	1900	700	1120
11	November	1200	2602	1100	1335
12	December	3500	3600	5850	4975

Table 4. Tesla Model S Sales Data⁷

1. Use the data in Table 4 to calculate a monthly adjustment factor and develop a monthly forecast for 2018 for the Model S (round to the whole car).

	2018
January
February
March
April
May
June
July
August
September
October
November
December

1. Using the actual data for 2018, compute the Mean Absolute Deviation and bias for this forecast model.

Actual Sales	2018
January	800
February	2050
March	2922

Table 5. 2018 Tesla Model S Sales Data⁶