Page 277 - F2 - MA Integrated Workbook STUDENT 2018-19

Statistical techniques

5.5 Seasonal variations

Once the trend has been identified it is possible to calculate the seasonal variations
from the trend. This is how much the data varies from the trend line.

There are two methods:

Additive model:

Using an additive model, variations are expressed in absolute terms with above and
below average figures shown by using a plus or minus sign respectively.

Example 6

Calculate the seasonal variation for the following set of data using the additive
model.

Seasonal
Month Value Trend
variation
Jan 12

Feb 26 19 26 – 19 = +7

Mar 19 20 19 – 20 = –1

Apr 15 21 15 – 21 = –6

May 29 22 29 – 22 = +7

Jun 22 23 22 – 23 = –1

Jul 18 24 18 – 24 = –6

Aug 32 25 32 – 25 = +7

Sept 25

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