251. MA

Moving average

i.e.,

Always stationary. Invertible if roots of lie outside the unit circle.

Parameters: , ,
Orders:

Example:

Given

  • Order:
  • Parameters: ,
  • Initial innovation:
  • Data:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
12 10 8 11 14 12 9 13 16 14 11 15 18 16 13 17

Step 1 — formula

Substitute into the MA recursion:

Forecast (set ):

Innovation:

Step 2 — apply at

Plug in , , and :

Step 3 — iterate

Each row uses the previous innovation . Values rounded to 4 decimal places.

1 12
2 10
3 8
4 11
5 14
6 12
7 9
8 13
9 16
10 14
11 11
12 15
13 18
14 16
15 13
16 17
17

Like AR(1), MA(1) cannot capture the trend or seasonality in .