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-600<br />

-700<br />

-800<br />

Loglikelihood<br />

-900<br />

-1000<br />

-1100<br />

-1200<br />

1 2 3 4 5 6 7<br />

k (the Number <strong>of</strong> States)<br />

Loglikelihood AIC BIC<br />

Figure 6.11: Loglikelihood, AIC and BIC against the number <strong>of</strong> states <strong>for</strong> the restricted<br />

covariance <strong>multivariate</strong> Poisson <strong>hidden</strong> Markov model<br />

Table 6.9 contains the parameter estimates and the bootstrapped standard errors <strong>for</strong> the<br />

independent model with five states. The calculation details <strong>of</strong> the bootstrapped standard<br />

errors were given in section 5.5. Here the bootstrap standard errors were considered<br />

because <strong>of</strong> the small sample size (McLachlan et al., 2000), and there<strong>for</strong>e, the asymptotic<br />

standard errors were not valid. Special care was taken to avoid the label switching (Brijs<br />

et al., 2004). This problem can be avoided by adding the relevant constraints,<br />

p1 ≤ p2<br />

≤ ... ≤ p j<br />

to the optimization algorithm ( p<br />

j<br />

’s are the posterior means <strong>of</strong> each<br />

127

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