New Delhi, Oct. 26 -- More data may not mean better decisions. In 1974, Paul Slovic, a psychologist and decision-science guru, performed an experiment on horse handicappers: i.e., professional predictors of horse racing outcomes. The handicappers were tasked with predicting the winner of 40 races. For each horse, 40 attributes were collected. Four rounds of prediction were to be made by these handicappers.

In round 1, each handicapper got to choose five attributes to predict the winner. They were also asked to comment on their confidence in their predictions. If they had picked a horse at random, their success rate would have been 10%, since each race had 10 horses. But in round 1, the correct-prediction rate was 17%, implying that the f...