SURVIVOR S HIP BI A S

D r awing c o ncl u sion s f r om an incom ple t e set of d a t a,
becau se tha t d a t a has ‘surv ived’ s ome sel e ction c rit eria.

W hen analyzing data, it ’s important to ask yourself what
data you don ’ t have. S ometimes, the full picture is obscured
because the data you’ ve got has survived a selection of some
sort. F or example, in W WII, a team was asked where the best
place was to fit armour to a plane. The planes that came
back from battle had bullet holes everywhere except the
engine and cockpit. The team decided it was best to fit
armour where there were no bullet holes, because planes
shot in those places had not returned.