When more data makes you more wrong

In a one-day international against Australia last year, Ben Stokes was dismissed for ‘obstructing the field’, a rule rarely invoked in-cricket. The bowler had thrown the ball towards the wicket (and hence near Stokes’s head) in an attempt to run him out. Stokes raised his hand and deflected the ball. After some discussion between the two on-field umpires, and a referral to the third umpire, Stokes was given out.

What was most interesting was the difference in the conclusions people reached depending on whether they watched the replay in real time or in slow motion (you can find both on YouTube). Seen at speed, his raising of his hand looked nothing more than an involuntary and instinctive act of self-defence. Viewed in slow motion (as the third umpire saw it), it seemed a wilful and deliberate act of wicket–preservation. In the first instance, everything happened so quickly that it seemed impossible that Stokes had time to think; in slow motion it seemed impossible that he hadn’t.

But none of this matters compared with the effects when slow-motion replays are used in criminal courts. A recent University of-Chicago experiment showed subjects video of a bungled robbery in which a shopkeeper was shot dead: those ‘juries’ shown a slow-motion replay were more than three times as likely to convict as those who saw events at the correct speed. The effect diminished when the footage was shown at both speeds, but persisted: such juries were still one and a half times more disposed to find the gunman guilty.

Usually new technology works in the interests of justice. Advances in DNA fingerprinting have not only helped solve countless crimes but have exonerated thousands of wrongfully accused people worldwide. Such advances are also a powerful deterrent against committing crimes in the first place (especially for people like me who hate cleaning.