More data makes for better economic policy, right? Lessons from 20th-century India and Hong Kong suggest the opposite is true.

Sir John Cowperthwaite was Hong Kong’s financial secretary from 1961-71 and is widely credited for the prosperity Hong Kong enjoys today. An ardent free-marketeer, Cowperthwaite believed that government should not try to manage the economy. One salient feature of Cowperthwaite’s policies: His administration didn’t collect any economic data during his tenure. Not even gross domestic product was calculated....