| Abstract: | This paper studies asymptotic properties of the quasi maximum likelihood and weighted least squares estimates (QMLE and WLSE)
of the conditional variance slope parameters of a strictly unstable ARCH model with periodically time varying coefficients
(PARCH in short). The model is strictly unstable in the sense that its parameters lie outside the strict periodic stationarity
domain and its boundary. Obtained from the regression form of the PARCH, the WLSE is a variant of the least squares method
weighted by the square of the conditional variance evaluated at any fixed value in the parameter space. In calculating the
QMLE and WLSE, the conditional variance intercepts are set to any arbitrary values not necessarily the true ones. The theoretical
finding is that the QMLE and WLSE are consistent and asymptotically Gaussian with the same asymptotic variance irrespective
of the fixed conditional variance intercepts and the weighting parameters. So because of its numerical complexity, the QMLE
may be dropped in favor of the WLSE which enjoys closed form. |
