Economic Models - Convex Optimization

Economic Models - Convex Optimization Economic Models - Convex Optimization

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A Novel Method of Estimation Under Co-Integration 35 The series { ∆xi}, { ∆ 2 x i }, and { ∆ 3 x i } Figure 2. Differences of the NI series {x i }. Using the series {x i } as shown in Table 1, we can easily verify from the corresponding graph, that even for n = 5, the series { 5 x i } is not stationary. In Fig. 2, the series {x i }, { 2 x i }, and { 3 x i } are presented, for a better understanding of this situation. We will call the variables, which belong to this category near the integrated (NI) (Banerjee et al., 1993, p. 95) series. To trace that a given series is NI, we may run the regression: x i = β 1 + β 2 x i−1 + β 3 t i + q∑ β j+3 x i−j + u i (24) which is a re-parametrized AR(q) with constant, where we added a trend too. As shown in Eq. (17), the value of q is set such that the noises u i to be white. A comparatively simple way for this verification is to compute the residuals û i and to consider the corresponding Ljung-Box Q statistics and particularly their p-values, which should be much greater than 0.1, to say that no autocorrelation (AC) is present. On the other hand, if we trace heteroscedasticity, this is a strong indication that we have a NI series. For the data presented in Table 1, we found that q = 2. The corresponding Q statistics (Column 4) together with p-values are presented in Table 2. We see that for all k (column 1), the corresponding p-values (column 5) are greater than 0.1. But, if we look at the residuals graph (Fig. 3), we can verify the presence of heteroscedasticity. j=1

36 Alexis Lazaridis Table 2. Residuals: Autocorrelations, PAC, Q statistics and p-values. Autocorrelation (AC), partial autocor coefficients (PAC) Q statistics and p values (prob). Values AC PAC Q Stat(L-B) p value Q Stat(B-P) p value of k 1 0.040101 0.040101 0.072482 0.787756 0.067540 0.794952 2 −0.061329 −0.063039 0.246254 0.884151 0.225515 0.893367 3 −0.008189 −0.003064 0.249432 0.969240 0.228331 0.972891 4 −0.285494 −0.290504 4.213238 0.377916 3.651618 0.455202 5 0.042856 0.072784 4.304969 0.506394 3.728756 0.589090 6 0.099724 0.058378 4.815469 0.567689 4.146438 0.656867 7 −0.151904 −0.167680 6.033816 0.535806 5.115577 0.645861 8 −0.007846 −0.069642 6.037162 0.643069 5.118163 0.744875 9 0.001750 0.023203 6.037333 0.736176 5.118291 0.823877 10 0.109773 0.165620 6.733228 0.750367 5.624397 0.845771 11 0.134538 0.022368 7.812250 0.730017 6.384616 0.846509 12 −0.029101 −0.048363 7.864417 0.795634 6.420185 0.893438 13 −0.074997 −0.028063 8.222832 0.828786 6.656414 0.918979 14 −0.084284 −0.017969 8.691681 0.850280 6.954772 0.936441 15 −0.113984 −0.104484 9.580937 0.845240 7.500452 0.942248 16 −0.081662 −0.157803 10.05493 0.863744 7.780540 0.955133 17 −0.001015 −0.005026 10.05501 0.901288 7.780582 0.971016 18 −0.053178 −0.056574 10.27276 0.922639 7.899356 0.980097 Figure 3. The residuals from Eq. (24) (q = 2).

36 Alexis Lazaridis<br />

Table 2.<br />

Residuals: Autocorrelations, PAC, Q statistics and p-values.<br />

Autocorrelation (AC), partial autocor coefficients (PAC) Q statistics and p values (prob).<br />

Values AC PAC Q Stat(L-B) p value Q Stat(B-P) p value<br />

of k<br />

1 0.040101 0.040101 0.072482 0.787756 0.067540 0.794952<br />

2 −0.061329 −0.063039 0.246254 0.884151 0.225515 0.893367<br />

3 −0.008189 −0.003064 0.249432 0.969240 0.228331 0.972891<br />

4 −0.285494 −0.290504 4.213238 0.377916 3.651618 0.455202<br />

5 0.042856 0.072784 4.304969 0.506394 3.728756 0.589090<br />

6 0.099724 0.058378 4.815469 0.567689 4.146438 0.656867<br />

7 −0.151904 −0.167680 6.033816 0.535806 5.115577 0.645861<br />

8 −0.007846 −0.069642 6.037162 0.643069 5.118163 0.744875<br />

9 0.001750 0.023203 6.037333 0.736176 5.118291 0.823877<br />

10 0.109773 0.165620 6.733228 0.750367 5.624397 0.845771<br />

11 0.134538 0.022368 7.812250 0.730017 6.384616 0.846509<br />

12 −0.029101 −0.048363 7.864417 0.795634 6.420185 0.893438<br />

13 −0.074997 −0.028063 8.222832 0.828786 6.656414 0.918979<br />

14 −0.084284 −0.017969 8.691681 0.850280 6.954772 0.936441<br />

15 −0.113984 −0.104484 9.580937 0.845240 7.500452 0.942248<br />

16 −0.081662 −0.157803 10.05493 0.863744 7.780540 0.955133<br />

17 −0.001015 −0.005026 10.05501 0.901288 7.780582 0.971016<br />

18 −0.053178 −0.056574 10.27276 0.922639 7.899356 0.980097<br />

Figure 3. The residuals from Eq. (24) (q = 2).

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