What Data Can’t Do

Hannah Fry in The New Yorker: “Tony Blair was usually relaxed and charismatic in front of a crowd. But an encounter with a woman in the audience of a London television studio in April, 2005, left him visibly flustered. Blair, eight years into his tenure as Britain’s Prime Minister, had been on a mission to improve the National Health Service. The N.H.S. is a much loved, much mocked, and much neglected British institution, with all kinds of quirks and inefficiencies. At the time, it was notoriously difficult to get a doctor’s appointment within a reasonable period; ailing people were often told they’d have to wait weeks for the next available opening. Blair’s government, bustling with bright technocrats, decided to address this issue by setting a target: doctors would be given a financial incentive to see patients within forty-eight hours.

It seemed like a sensible plan. But audience members knew of a problem that Blair and his government did not. Live on national television, Diana Church calmly explained to the Prime Minister that her son’s doctor had asked to see him in a week’s time, and yet the clinic had refused to take any appointments more than forty-eight hours in advance. Otherwise, physicians would lose out on bonuses. If Church wanted her son to see the doctor in a week, she would have to wait until the day before, then call at 8 a.m. and stick it out on hold. Before the incentives had been established, doctors couldn’t give appointments soon enough; afterward, they wouldn’t give appointments late enough.

“Is this news to you?” the presenter asked.

“That is news to me,” Blair replied.

“Anybody else had this experience?” the presenter asked, turning to the audience.

Chaos descended. People started shouting, Blair started stammering, and a nation watched its leader come undone over a classic case of counting gone wrong.

Blair and his advisers are far from the first people to fall afoul of their own well-intentioned targets. Whenever you try to force the real world to do something that can be counted, unintended consequences abound. That’s the subject of two new books about data and statistics: “Counting: How We Use Numbers to Decide What Matters” (Liveright), by Deborah Stone, which warns of the risks of relying too heavily on numbers, and “The Data Detective” (Riverhead), by Tim Harford, which shows ways of avoiding the pitfalls of a world driven by data.

Both books come at a time when the phenomenal power of data has never been more evident. The covid-19 pandemic demonstrated just how vulnerable the world can be when you don’t have good statistics, and the Presidential election filled our newspapers with polls and projections, all meant to slake our thirst for insight. In a year of uncertainty, numbers have even come to serve as a source of comfort. Seduced by their seeming precision and objectivity, we can feel betrayed when the numbers fail to capture the unruliness of reality.

The particular mistake that Tony Blair and his policy mavens made is common enough to warrant its own adage: once a useful number becomes a measure of success, it ceases to be a useful number. This is known as Goodhart’s law, and it reminds us that the human world can move once you start to measure it….(More)”.