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6. The Notion of parameter redundancy pertains to the situation when AR and MA characteristic polynomials 0(z) and share 0(z) share a common factor, in which case model may be simplified. Determine which of the following models are parameter redundant: I. X+ = 1Xt-1+ 2+ - 1Zt-1; II. Xt = Xt-1 + Zt - Zt-2; III. X+ = - Xt-1 - 6X4-2 + 2+ + 241 + 12272. 6. The Notion of parameter redundancy pertains to the situation when AR and MA characteristic polynomials 0(z) and share 0(z) share a common factor, in which case model may be simplified. Determine which of the following models are parameter redundant: I. X+ = 1Xt-1+ 2+ - 1Zt-1; II. Xt = Xt-1 + Zt - Zt-2; III. X+ = - Xt-1 - 6X4-2 + 2+ + 241 + 12272