# 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.***

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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.