t Copula Fit

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Trambak
Trambak 2012-3-8
I am generating 100 t copula radom numbers with Rho=0.4 and Nu =5, using the copularnd function. Then I fit these random numbers back to a t copula. I do this 1000 times and I expect to see the distribution of Nu to be centered around 5. However, the estimated value of Nu takes very high values in many occasions. Any reasons?

回答(1 个)

Andrew Newell
Andrew Newell 2012-3-8
That's just a consequence of the small sample size, and consistent with the 95% confidence estimate ( nuci ) you get for nuhat if you use the following commands:
rho = 4.5; nu = 5; N=100;
U = copularnd('t',0.4,5,N);
[rhohat,nuhat,nuci] = copulafit('t',U)
If you use N=1000, you'll see much tighter bounds on nuhat.

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