The Outside View: Base Rates Beat Forecasts

"The inside view asks: what is special about this situation? The outside view asks: what usually happens in situations like this?" — Michael Mauboussin

Mauboussin turns a well-known finding from behavioural science into a practical investing tool: the outside view.

Most analysts build forecasts from the inside — detailed, company-specific models full of bespoke assumptions. That feels rigorous, but it is reliably overconfident. The outside view starts somewhere else: with the base rate — what actually happened to the broad set of similar businesses.

For example:

1. What share of high-growth companies sustain more than 20% revenue growth for ten years? Historically, only a small fraction.
2. What share of very high-return businesses keep those returns for a decade? A minority.
3. What share of dominant incumbents survive a major technology shift intact? Again, relatively few.

The outside view does not replace company-specific analysis — it anchors it. You start from the base rate and then adjust towards your particular case, rather than building from scratch and accidentally assuming "this time is different". The discipline is simply: look up the base rate before you model.

Illustrative example: forecasts versus reality

Studies have found that professional analysts, on average, forecast long-term earnings growth at roughly twice the rate companies actually deliver over time. The inside view, in aggregate, is far too optimistic; starting from the historical base rate corrects much of that bias at the source.