Sunday, January 09, 2011

'Individuals and statistics'

This seems like a partic- ularly Escher- esque bit of news judgment: People don't understand that a number doesn't necessarily mean anything just because it looks big, so it becomes a frontpage story* because editors don't understand that a number doesn't necessarily mean anything just because it looks big, so people see a frontpage story confirming their suspicions and refuse to believe that the next big number doesn't ... I am he and you are he and you are me and we are all together.

Anyway! These stories** showed up on front pages just in time -- coincidence, or what? -- for the first Bad Science column of the year by the stellar Ben Goldacre:

'Six hundred pregnancies despite contraceptive implant," said the BBC. "500 fall pregnant after having contraceptive implant," said the Express. "Contraceptive implant alert," said the Daily Mail: "Hundreds of women fall pregnant after birth control fails."

The story first broke on Channel 4, and it's still not entirely clear why it's the biggest medical story so far this year.

Because ... NUMBERS! Put a bit differently, because when somebody yells "Seven!" at the newsroom, the response tends to be "OMG Seven!!!" rather than the sensible if less frontworthy "Seven of what?" Ben's going to help you put a stop to that:

... Six hundred pregnancies sounds like a big number, but there is no way to know what it means unless we know how many women had Implanon, and for how long. The device was first launched in 1999, so that makes 60 pregnancies a year, which feels like a smaller number, but that is still not enough information. The figure that epidemiologists use for context is "person-years-at-risk".

The Medicines and Healthcare products Regulatory Agency estimates that 1.355m Implanon implants have been sold. Each implant lasts three years which gives a total exposure time of 4.06m women-years at risk.

So 584 unplanned pregnancies means there were 1.4 reported for every 10,000 women with Implanon implants per year, a failure rate of 0.014% per year. It means implants are still the most reliable form of contraception.

"SEVEN!" is a lot less exciting, hedwise, when the deck says "Still comes after six, before eight."

Back with our 584 unwanted pregnancies, we see the difference between individuals and statistics. For some of the people who got pregnant, from their end of the telescope, this is a disaster. Some cases may well have been avoidable. Some will want financial compensation, and you will have your own views on the state's role in this.

But for a potential user of the implant, or a news editor, looking at the whole population, at its worst, it still seems to be one of the most effective forms of contraception available even though this particular implant had a problem with insertion – which has already been improved on.

I think that's a humane way of noting that, while "data" may be a plural, it isn't the plural of "anecdote." There's nothing wrong with responding humanly to stories of personal disaster; that's where the first half of "comfort the afflicted and afflict the comfortable" comes from. But different ways of framing news can affect attitudes and decision-making,*** and it's very much worth asking whether it's a good idea to comfort one set of afflicted people by risking an increase in the overall rate of affliction.****

I wonder if anyone has thought about syndicating Ben Goldacre in the States. In a world of columnists who are experts on being experts, it's refreshing to read one who's actually an expert on a topic.

* Can't find it at the originating paper's Web site; this link takes you to a different version.
** The first is from the Las Vegas Review-Journal, and I don't know whether to attribute the hed's tone to random effects or to corporate distrust of the Al-Maobama regime. (The LVR-J remains an outlet for the entertainingly unhinged Sherman Frederick.) The second is from the Charlotte Observer, which not only ran a centerpiece saying its centerpiece wasn't news but made a complete hash of the "experts" explanation. Technology doesn't tell "us" what "scientists already know"; technology just makes it easier to disseminate information without context.
*** That's a middle-range effect, not a big effect.
**** This observation is meant to encompass not just the lab-coat world (contraception, childhood vaccines, climate science and the like) but the realm of social science -- specifically, the paranoid race-baiting beloved of some press sectors.

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Blogger Strayhorn said...

"women fall pregnant"

I've never seen that construction. Strange.

11:25 AM, January 12, 2011  

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