The Wisdom of Crowds

Francis Galton, a Victorian scientist, statistician, and polymath, touring the West of England Fat Stock and Poultry Exhibition, came across a competition to guess the weight of an ox. Visitors could, for sixpence, buy a ticket entitling them an estimate at the animal’s weight. They were to fill out their name, address and their guess in pounds, with the most accurate entries assured of prizes.

Galton persuaded the organisers, once the contest was over, to lend him all the chits – some 800 in number – and he set about analysing them. Writing later in the scientific journal Nature, Galton noted that while some in the group, like butchers and farmers, had expert knowledge, many were, as he put it, ‘guided by their own fancies’. 

Galton’s insight was to treat the group as though it were a single individual. The question then became: how could he best capture its collective estimate? He reasoned that arranging all the entries in ascending order and identifying the middle value – the median – would provide a representative answer. 

Discarding the cards that were illegible left him with 787 estimates. The middle value, which Galton took to be representative of the group, was 1,207lb. The actual weight turned out to be 1,198lb. Galton noted this collective answer – he called it the vox populi, meaning ‘voice of the people’ – was within 1% of the true answer. The crowd were virtually spot on. The result surprised him, writing, with characteristic Victorian understatement, that it was ‘more creditable to the trustworthiness of a democratic judgment than might have been expected’.The article would be one of his last. Galton was well into his eighties when he toured the show, and he died just four years later.

And there the incident might have faded into obscurity. But a century later the story gained a second life. James Surowiecki, a journalist with The New Yorker, discovered Galton’s article and brought it back into the spotlight, through a best-selling book about the power of collective intelligence. In doing so, he popularized the phenomenon Galton had uncovered, giving it the name by which it is now widely known – The Wisdom of Crowds.