This is the short edition of More or Less, first broadcast on the BBC World Service.

Hello and welcome to More or Less on the BBC World Service.

We're a programme that looks at the numbers in the news and in life and I'm Tim Harford.

Protests have spread across the United States over the last few weeks.

The protesters have been registering their feelings about incidents where police have shot and killed black men.

The most high profile recent incidents resulted in the deaths of Alton Sterling and Philando Castle,

and the protesters feel that minorities are being disproportionately targeted by the police.

On top of this, at a recent protest in Dallas, a gunman shot and killed five police officers.

Feelings are running high for understandable reasons.

But what can the numbers tell us about the issue?

How many people do police officers kill each year in the United States and how many police

officers are killed. Let's start with a number of people killed by the police.

We decided to take a look at what the official data say and found that information on the number is remarkably

unreliable. Here's James Comi, the director of the FBI speaking in the House of Representatives

last year, broadcast on C-SPAN.

We can't have an informed discussion because we don't have data.

People have data about who went to a movie last weekend or how many books were sold or

how many cases of the flu walked into an

emergency room and I cannot tell you how many people were shot by police in the

United States last month last year or anything about the demographics and that's a

very bad place to be.

Because the authorities weren't collecting the data, other organizations have stepped in to fill

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