Time Series Analysis and Forecasting
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Time Series Analysis and Forecasting Coursework Plot 1. Time series plot of IBM price The time series plot shows an increasing trend, no seasonal or cyclical components. The autocorrelation function (acf) has high auto correlations that decrease slowly- giving the shape of a 'thick wedge'- this pattern is indicative of a trend. We cannot use our models because of the presence of the trend; this must be removed by differencing the series with a lag of 1. Plot 2. Time series plot of differenced IBM prices The plot and acf now show no pattern in the differenced series, we now have a stationary series on which to use our models. The first autocorrelation is significantly different from zero (T=2.43>2) and all the other autocorrelations lie within the confidence limits so this suggests that MA (1) model can be used for the differenced series. Only the first partial autocorrelation (pac) is significantly different from zero (T=2.43>2)...


