Investigate Time Series Model Residuals
Having found the model that successfully describes the time series of interest, the fit residual is expected to be a Gaussian white noise process.
Monthly data of accidental deaths in USA from 1973 to 1978.
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Fit an ARMA model to the data.
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Autocorrelation, partial autocorrelation, and Ljung–Box plots suggest correlation at lag 12.
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Fit a seasonal ARMA model with seasonality of 12.
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ACF, PACF, and Ljung–Box plots indicate that residuals are likely a white noise.
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Selection criteria favor the seasonal model over the non-seasonal one.
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