I want to forecast a time series Y using a model that includes previous values of Y and an exogenous time series X using a transfer function. The standard procedure as described in Box and Jenkins and numerous other references is to first fit an ARIMA model to X. Use the ARIMA model to computer residuals for X and then apply the same ARIMA function to Y to compute residuals for Y. The cross correlation between these two sets of residuals then should allow discovery of the structure of the transfer function that relates X to Y. How can I do this in R? I know how to use the ts package to fit ARIMA models. Is it possible to use the "filter" function from the ts package to help compute the proper residuals for Y? I've read (and reread) the help file on "filter" and tried to apply it but I must be missing something. How can I use "filter" to handle both the AR and MA components? Or am I on the wrong track?

Rick B.

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