The Mathematical Murder of Innocence

By Michael Carter — For every mystery/crime fiction lover, there are books that hit the sweet spot of their special interests. There are the cozies with the knitting patterns and recipes. There are election fraud novels for political junkies. There are the gritty, down and dirty books for people who don’t get enough of that in the daily news. Books featuring computer nerds, financial advisers, art appraisers, cat sitters, on and on.

The Mathematical Murder of Innocence, not the first book I’ve read about a math whiz, is an eye-opener. It was inspired by real-life cases in Britain, in which women were convicted of killing their infants based on a really faulty understanding of statistics. Most people—and that apparently includes lawyers and judges and juries—don’t have a good grasp of how statistics work. You might think calculating odds (except, perhaps in horse-racing) is a rather straightforward exercise. Yet, how you calculate them makes all the difference, and the results can fly in the face of “common sense.”

For example, if you toss a coin that comes up heads ten times in a row, you might be inclined to take the bet that you’ll get tails on the next toss. Don’t do it! Unless the coin is faulty, each toss is an independent event and the odds of heads or tails is 50-50 every time. Likewise, you might estimate you’d need a group of at least 100 or even 200 people to make it likely two of them would have the same birthday. You’d be wrong. You only need 23 people to have a 50-50 chance of matching birthdates.

Luckily for the fictional Sarah Richardson, the woman standing trial in Michael Carter’s novel, on her jury is engineer Martin Fielding. Richardson’s two infant sons have died of cot death (Sudden Infant Death Syndrome in the US). Dr. Michael Goodwin, the prosecution’s expert witness, says that, given the relative rarity of cot death (one in every 8,500 births), the odds of losing two children that way are one in 72 million (8,500 x 8,500). “One death is a tragedy; two deaths are murder,” he says. But juror Fielding believes the correct number is more like one in 18 and sets out to prove it.

Set aside for a moment any skepticism that a juror would repeatedly burst out his objections to a witness’s testimony. Then set aside your doubts (perhaps they could be expressed as odds, like one in a thousand) that Fielding would be invited to take over the questioning of Dr. Goodwin. Once you accept those long odds—the outbursts, the cross-examination—the story becomes a delightful takedown of a pompous and dangerous man. A bit of a deep dive into statistics, but . . . it might save someone’s life.

The photo is from a 1990s British courtroom drama series, Kavanagh, QC, starring John Thaw. Excellent entertainment!

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