Tuesday, 11 June 2013

Is the Director of Public Prosecutions innumerate?

It varies a lot, so Mr Starmer couldn't average it
Listening to the Today programme on Radio 4 a few days ago (5 June), I couldn't help wonder if the Director of Public Prosecutions, the exotically named Keir Starmer, struggles with numbers and particularly with statistics.

There were two issues with Mr Starmer's answers. The interviewer was trying to get Starmer to put a percentage on the point at which the prosecution service would take a case forward. What was the probability of success required before prosecuting? Starmer couldn't reply. There just, he said, had to be a reasonable chance of success. The actual percentage could vary from case to case. That's really not good enough. What does 'a reasonable chance' mean? There is an implied number in there - but he's not admitting what it is. And if it does vary from case to case, fine. But what are the criteria? It's fair enough to say there isn't a consistent percentage of likelihood across different types of case (though there needs to be a clear reason for varying it), but there needs to be a good logical reason for doing this. Without it, the justice system is anything but transparent and potential subject to misuse.

The second problem Mr Starmer has is that he clearly doesn't understand what an average is. He was asked how long it took them to consider a case and replied 'It varies a lot, so we can't come up with a average.' Well, no Mr Starmer, this is exactly when you can come up with an average. If it was always 21 days you wouldn't need an average - it is only if there is variability that you need one. Of course if it is an interesting distribution you need to tell us a bit more - the median, perhaps, and what the distribution is like. But this provides no excuse for hiding behind vagueness.

There are two possibilities here. Either Mr Starmer is innumerate or he was trying to conceal things with deliberate vagueness. Taking the kind view that no deception was involved, perhaps we can make sure that when he is replaced we get someone who has familiarity with the basics of statistics and can make sure his department is acting fairly and logically - impossible without having a grasp of those numbers.

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