Forecasting or Predicting is the act of making statements about what will happen in the future (and in some cases, the past) and then scoring the predictions. Posts marked with this tag are for discussion of the practice, skill, and methodology of forecasting. Posts exclusively containing object-level lists of forecasts and predictions are in Forecasts. Related: Betting.

Above all, don’t ask what to believe—ask what to anticipate. Every question of belief should flow from a question of anticipation, and that question of anticipation should be the center of the inquiry.
—Making Beliefs Pay Rent

Forecasting allows individuals and institutions to test their internal models of reality. A good forecaster can have confidence in future predictions and hence actions in the same area as they have a good track record in. Organisations with decision-makers with good track records can likewise be more confident in their choices.

Forecasting Techniques

Forecasting is hard but many top forecasters use common techniques. This suggests that forecasting is a skill that can be learnt and practised.

Base rates

Reference Class Forecasting on Wikipedia

Suppose we are trying to find the probability that an event will occur within the next 5 years. One good place to start is by asking "of all similar time periods, what fraction of the time does this event occur?". This is the base rate.

If we want to know the probability that Joe Biden is President of the United States on Nov. 1st, 2024, we could ask

What fraction of presidential terms are fully completed (last all 4 years)? The answer to this is 49 out of the 58 total terms, or around 84%.
On the other hand, we know that Biden has already made it through 288 days of his term. If we remove the 5 presidents who left office before that, there are 49 out of 53 or around 92%.
But alternately, Joe Biden is pretty old (78 to be exact). If we look up death rate per year in actuarial tables, it's around 5.1% per year, so this leaves him with a ~15% chance of death or a 85% chance of surviving his term.

These are all examples of using base rates. [These examples are taken from Base Rates and Reference Classes by jsteinhardt.]

Base rates represent the outside view for a given question. They are a good place to start but can often be improved on by updating the probability according to an inside view.

Note that there are often...

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