Solution
The Missing Bullet Holes
Show the problem again
In WWII, returning aircraft showed dense bullet holes on the wings and fuselage but few on the engines. The military proposed reinforcing the areas with the most holes. Statistician Abraham Wald recommended the opposite. Where should the armor go?
Worked solution
On the engines: the planes hit there never made it back. The data suffer survivorship bias: only surviving aircraft are observed. Holes on wings and fuselage indicate damage a plane can survive; the near-absence of engine hits among returners means engine hits were disproportionately fatal, censoring those planes from the sample. Wald's insight (analyze the missing data, not just the observed) generalizes to fund performance, "success secrets," and any sample filtered by outcome.
Source: From Abraham Wald's aircraft-survivability work for the Statistical Research Group in the Second World War; the canonical survivorship-bias example. Statement written for AxiomIQ.