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Problems<br />

Figure 6-19<br />

The differenced deaths and<br />

serious injuries on UK<br />

roads {Xt Yt − Yt−12},<br />

showing the fitted<br />

GLS regression line.<br />

Problems 219<br />

updated to<br />

Xt −328.45gt + Nt, (6.6.18)<br />

with the fitted MA(12) model for the residuals also displayed. After several iterations<br />

(each iteration is performed by pressing the MLE button) we arrive at the model<br />

with<br />

Xt −328.45gt + Nt, (6.6.19)<br />

Nt Zt + .219Zt−1 + .098Zt−2 + .031Zt−3 + .064Zt−4 + .069Zt−5 + .111Zt−6<br />

+ .081Zt−7 + .057Zt−8 + .092Zt−9 − .028Zt−10 + .183Zt−11 − .627Zt−12,<br />

where {Zt} ∼WN(0, 12, 581). The estimated standard deviation of the regression<br />

coefficient estimator is 49.41, so the estimated coefficient, −328.45, is very significantly<br />

negative, indicating the effectiveness of the legislation. The differenced data<br />

are shown in Figure 6.19 with the fitted regression function.<br />

6.1. Suppose that {Xt} is an ARIMA(p, d, q) process satisfying the difference equations<br />

-600 -400 -200 0 200<br />

φ(B)(1 − B) d Xt θ(B)Zt, {Zt} ∼WN 0,σ 2 .<br />

1976 1977 1978 1979 1980 1981 1982 1983 1984 1985

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