The stats behind date-rape drug detectors - Macleans.ca

The stats behind date-rape drug detectors

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A detection kit for the most common date rape drugs is going on sale throughout Canada shortly, according to the Montreal Gazette. The Gazette did not have to look far to find someone to denounce the ethical premise of such apparatuses: a spokesman for a Vancouver women’s shelter said “This is a cynical attempt to make some money and shame on the company for feeding off the fear that women, reasonably, have of being raped.”

I suppose most of us would respond with something very like Adam Smith’s classic formulation: we are not to look to a “lack of cynicism” for the answers to our social problems, any more than we look to the fellow-feeling of the butcher and the baker to provide us with sustenance. If something like the Drink Detective—which consists of a pipette and three pieces of treated paper—enabled us to end drug-facilitated rape tomorrow, that would be a very good thing indeed.

Unfortunately, almost 100% of barroom beverages contain a highly effective substance that diminishes inhibitions and impairs memory. More to the point, it is odd that a test for “date rape drugs” other than ethanol should be criticized on the premise of its effectiveness without any attempt at an inquiry into that effectiveness. The Drink Detective website, by itself, doesn’t encourage confidence. It features a supposedly independent, but thinly sourced, “technical report” into the accuracy of the kit. One press release on the site, perhaps in a ham-handed attempt to double the market for the product, recycles the urban legend that “In some countries, it is even possible to be drugged and incapacitated so that organs, such as kidneys, can be surgically removed and sold.”

You are probably wondering whether there have been any peer-reviewed studies of the Drink Detective, and why, if there are, they aren’t mentioned on the “Science” page of the product’s website. The answer to your first question is “Yes”. And you probably already have a potential answer to the second if you’ve studied statistics.

An team of public health researchers in Liverpool published a study of the Drink Detective in the journal Addiction in 2006. They found that the Drink Detective was significantly superior to a rival product, and as a technical feat of fast, cheap detection of complex molecules, the kit deserves not just praise but wonder. But is it really of much use? The authors found that the overall sensitivity of the kit was about 69.0% and its specificity was 87.9%. In plainer English, this means that for every 100 samples of adulterated booze, the test will, on average, miss (100-69), or 31; and for 100 non-drugged drinks, the test will give (100-87.9), call it 12, false positives.

Women who are hyper-conscious of the possibility of drug-assisted rape will not be happy to hear that the Drink Detective gives a clean bill of health to almost one-third of drink-tampering sociopaths. But the false positives are a concern too: it would be easy to design a test that “caught” every single spiked drink if you didn’t care about specificity as well as sensitivity. (A heuristic of “Run straight home if a napkin becomes moistened when you dip it in your glass” would have 100% sensitivity.) In situations where the real odds of getting a spiked drink were as high as 1 in 100, a test with 88% specificity would still finger 12 innocents as toxic creeps for every 1 guilty man it identified. Even at a reasonable-sounding price per kit of $5.99, test fatigue seems likely under realistic circumstances.

The Drink Detective’s manufacturers had some specific gripes about the Liverpool test—complaining, for instance, that the testers’ use of pharmaceutical-grade GHB was inappropriate—but they had received the benefit of the doubt in at least one large, obvious way: the kit was put through its paces, not in a dimly-lit pub toilet by experimenters half-wrecked on Cosmos, but by sober scientists working in a laboratory. It is hard to disagree with the conclusion that “Use of drug detector kits by the public in the night-time environment…may create a false sense of security (false negatives) and undue concern (false positives) among kit users.” And the same could be said—to her credit, Daisy Kler of the Vancouver Rape Relief and Women’s Shelter does say it—about the overall focus on drug-facilitated sexual assault by strangers. No one is certain how often this really happens, and the best guess is “not very”.