Indian Journal of Science and Technology
Year: 2010, Volume: 3, Issue: 9, Pages: 1026-1031
Department of Mathematics, Pachaiyappa’s College for Men, Kancheepuram–631 501, TN, India
[email protected] ; [email protected]
Diagnostic checks have become a standard tool for identification of models before forecasting the data. The overall test for lack of fit for autoregressive moving average models proposed by Box and Pierce (1970) and a measure of lack of fit in time series models proposed by Ljung and Box (1978) are considered. In this paper, a modification is made and it is shown that a substantially improved approximation results from a simple improvement of this test. Cumulative periodogram check is also given.
Keywords: Time series, ARMA, ARIMA, forecasting.
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