Shopping habits, risky decisions and getting to grips with statistics

I’m sure Jen Reid didn’t intend to improve my shopping habits when she conceived the ‘Journal Club’ series on critical appraisal for Speech & Language Therapy in Practice – but that has been one outcome.

I picked up a pack of four leeks yesterday emblazoned with ‘Special offer! Only £1.70!’ But I paused as a little voice in my head said, “Check the figures and think about it. It’s up to you, not the shop, to decide if this is the best deal.” The loose leeks had a tiny little sign saying ‘£2.75 a kilo’. The four nicely packaged leeks weighed 500g. I did the maths - and swapped them over.

A new Cochrane Systematic Review concludes that people – whether health professionals or consumers – may make different decisions depending on the way risk statistics are presented. There are the usual caveats about more research being needed (and I won’t claim to have studied the whole review), but check out how the example given in the plain language summary (p.2) changes your own perceptions:
“You read that a study found that an osteoporosis drug cuts the risk of having a hip fracture in the next three years by 50% [relative risk reduction]. Specifically, 10% of the untreated people had a hip fracture at three years, compared with 5% of the people who took the osteoporosis drug every day for three years. Thus 5% (10% minus 5%) less people would suffer a hip fracture if they take the drug for 3 years [absolute risk reduction]. In other words, 20 patients need to take the osteoporosis drug over 3 years for an additional patient to avoid a hip fracture [number needed to treat].”

The authors conclude their findings suggest that “the formal education and training of health professionals apparently has no effect on their handling of statistical information” (p.26). It certainly doesn’t come easily to me but, as a teacher said at my older son’s parents’ evening, “He is used to being able to do things so, when they don’t come naturally, he just thinks he can’t do it. I tell him to take his time and to think it through, because he can. And then he does.”

I will keep trying to understand statistics because, when we are asking people to trust us to give them appropriate, evidence based information, an ability to look behind the headlines matters.

Jennifer Reid’s Journal Club series in Speech & Language Therapy in Practice has so far taken the mystery out of appraising expert opinion articles (Autumn 2010), qualitative research (Winter 2010) and systematic reviews (Spring 11). In Summer 11 she will tackle intervention.

Reference
Akl EA, Oxman AD, Herrin J, Vist GE, Terrenato I, Sperati F, Costiniuk C, Blank D, Schünemann H. Using alternative statistical formats for presenting risks and risk reductions. Cochrane Database of Systematic Reviews 2011, Issue 3. Art. No.: CD006776. DOI: 10.1002/14651858.CD006776.pub2.

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