Summary
In this introduction to time series forecasting, we learned that we need the data to autocorrelate to be useful for predictions. We have to plot the data and see whether it has seasonal or cyclical trends to learn whether past data influences the next period of data. Then, we need to use the Durbin-Watson statistical test to prove that the data is autocorrelated.
The forecast calculation uses the trending line of the regression model multiplied by the seasonal irregularity factor. This factor gives us the direction of the trending line based on the cyclical information of the past data. Use your experience to analyze whether the forecast returned by the model makes sense with the past data.
In the next chapter, we will start studying grouping statistics.