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Homework Statement
Calculate: PLIM (probability limit) [itex]\frac{1}{T} \sum^T_{t=2} u^2_t Y^2_{t-1} [/itex]
Homework Equations
[itex]Y_t = \rho Y_{t-1} + u_t, t=1,...T, |\rho| <1 [/itex] which the autoregressive process of order 1
[itex] E(u_t) = 0, Var(u_t) = \sigma^2[/itex] for t
[itex] cov(u_j, u_s) = 0[/itex] for j [itex]\neq s [/itex]
The Attempt at a Solution
I know that PLIM [itex]\frac{1}{T} \sum^T_{t=2} u^2_t Y^2_{t-1} = E[u^2_t Y^2_{t-1}] [/itex]
I have found [itex] Y_{t-1} = \sum^{T-1}_{j=0} \rho^j u_{t-1-j} [/itex]
Plugging in, I get [itex]E[u^2_t Y^2_{t-1}] = E[u^2_t (\sum^{T-1}_{j=0} \rho^j u_{t-1-j})^2]=E[(u_t (\sum^{T-1}_{j=0} \rho^j u_{t-1-j}))^2]=E[(\sum^{T-1}_{j=0} \rho^j u_{t-j} u_{t-1-j})^2]=\sum^{T-1}_{j=0} \rho^j E[(u_{t-j} u_{t-1-j})^2][/itex]
And I am stuck here because I don't know what to do with [itex]E[(u_{t-j} u_{t-1-j})^2][/itex] ??
Thank you in advance!
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