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1.      Arrange the data in a table by quarters and years.

2.      Calculate the average of quarters for years 1 and 5. Substract 5 from  and divide the result by 16. Call it net upward movement over 16 quarters, not 20. And get the average.

3.      calculate grand mean for every quarter

4.      Elliminate num by adding 1.5 num to Q1, 0.5 to Q2, -0.5 to Q3, -1.5 to Q5 - get the adjusted average.

5.      Calculate the mean of quartely grand means.

6.      Divide the quartely average by the whole average and get the seasonal pattern

7.      Divide original figgures by the seasonal pattern to get the seasonally adjusted data.

 year \ Quarte Q1 Q2 Q3 Q4 Average 1 100 70 60 90 80 2 120 85 70 110 3 150 105 85 130 4 170 125 100 155 5 190 150 120 180 160 average 146 107 87 133 Grand-118.3

Net-ward 06ve0ent = 80, Average num=5

 Adjust num 1.5x5 0.5x5 -0.5 -1.5 Ratio to gran 1.29 0.92 0.71 1.06 1.0(seasonal Estimation Q1 Q2 Q3 Q4 YEAR 1 77 75.6 83.9 84.8 2 92.4 91.8 97.9 103.7

It is essential to have the same number of quarters in every year. (ie not only first)

Awkward factors like easter

Changes in practice - holidays arrangement with Bank holidays

Do not use for more than 5 years