STA457H1 S-LEC5101 Time Series Analysis Quiz 2
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Department of Statistical Sciences
Time Series Analysis
STA457H1 S-LEC5101
STA457H1/STA2202H S-LEC0101 & STA457H1S LEC2001
Quiz 2
Q1. (a) Differencing adjacent terms of a time series can transform a non-stationary
series to a stationary series. Differencing is thus used as a filtering procedure in the study of non- stationary time series. The difference operator 又 is defined
by 又xt = xt - xt − 1 = (1 - B)xt , where B is the backshift operator. Prove that
higher-order differencing can be expressed as: 又n = (1 - B)n . (12 pts) (b) Write each of the model and express them in Backshift Operator notation:
(i) xt = 0.3xt − 1 + wt
(ii) xt = wt - 1.3wt − 1 + 0.40wt −2
(iii) xt = 0.50xt − 1 + wt - 0.30wt − 1 + 1.20wt −2
(iv) xt = 0.40xt − 1 + 0.45xt −2 + wt - 0.30wt − 1 + 0.25wt −2
(8 pts)
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2022-02-10