What can we forecast?
Before we move ahead, there is another aspect of time series forecasting that we have to understand—the predictability of a time series. The most basic assumption when we forecast a time series is that the future depends on the past. But not all time series are equally predictable.
Let's take a look at a few examples and try to rank these in order of predictability (from easiest to hardest), as follows:
- High tide next Monday
- Lottery numbers next Sunday
- The stock price of Tesla next Friday
Intuitively, it is very easy for us to rank them. High tide next Monday is going to be the easiest to predict because it is so predictable, the lottery numbers are going to be very hard to predict because these are pretty much random, and the stock price of Tesla next Friday is going to be difficult to predict, but not impossible.
NOTE
However, for people thinking that they can forecast stock prices with the advanced techniques covered in the book and get rich, that...