Philip Tetlock's superforecasting research identified the single biggest difference between accurate and inaccurate forecasters: the accurate ones start with the base rate. Before considering any specific details about a situation, they ask: historically, how often does this type of thing happen?
Why Base Rates Matter So Much
Human intuition is terrible at probability. We overweight recent, vivid, and emotionally salient information. Base rates — the actual historical frequency of similar events — anchor us to reality before we let the narrative take over.
Example: "Will this incumbent president win re-election?" Without base rates, you might anchor to the specific candidate's current poll numbers. With base rates, you start by knowing that incumbents historically win re-election about 65-70% of the time across mature democracies. That prior is your starting point — then you adjust for specific evidence.
The Outside View vs the Inside View
"The outside view asks: what is the base rate for situations like this? The inside view asks: what makes this situation special? Good forecasters use both — in that order."
— Daniel Kahneman, paraphrased
Applying Base Rates in Practice
- →Sports: look up historical win rates for similar seeding matchups, not just current form
- →Politics: check incumbent re-election rates, party advantage in similar constituencies
- →Finance: look at historical frequency of rate cut cycles, earnings surprise rates by sector
- →Entertainment: base rates for award nominees who won the most preliminary awards going in
- →Science/policy: how often do announced government policies actually pass without major amendment?
The base rate is your null hypothesis. You need a specific reason to deviate from it — not just a feeling that this time is different.
Most prediction market prices already incorporate publicly known base rates. Your edge comes from knowing more precise base rates, or from knowing that the market has incorrectly applied the reference class.