How to stop being so easily manipulated by misleading statistics

Curated on Posted on by Stefaan Verhulst

Q&A by Akshat Rathi in Quartz: “There are three kinds of lies: Lies, damned lies, and statistics.” Few people know the struggle of correcting such lies better than David Spiegelhalter. Since 2007, he has been the Winton professor for the public understanding of risk (though he prefers “statistics” to “risk”) at the University of Cambridge.In a sunlit hotel room in Washington DC, Quartz caught up with Spiegelhalter recently to talk about his unique job. The conversation sprawled from the wisdom of eating bacon (would you swallow any other known carcinogen?), to the serious crime of manipulating charts, to the right way to talk about rare but scary diseases.

In a sunlit hotel room in Washington DC, Quartz caught up with Spiegelhalter recently to talk about his unique job. The conversation sprawled from the wisdom of eating bacon (would you swallow any other known carcinogen?), to the serious crime of manipulating charts, to the right way to talk about rare but scary diseases.

 When he isn’t fixing people’s misunderstandings of numbers, he works to communicate numbers better so that misunderstandings can be avoided from the beginning. The interview is edited and condensed for clarity….
What’s a recent example of misrepresentation of statistics that drove you bonkers?
I got very grumpy at an official graph of British teenage pregnancy rates that apparently showed they had declined to nearly zero. Until I realized that the bottom part of the axis had been cut off, which made it impossible to visualize the (very impressive) 50% reduction since 2000.You once said graphical representation of data does not always communicate what we think it communicates. What do you mean by that?
Graphs can be as manipulative as words. Using tricks such as cutting axes, rescaling things, changing data from positive to negative, etc. Sometimes putting zero on the y-axis is wrong. So to be sure that you are communicating the right things, you need to evaluate the message that people are taking away. There are no absolute rules. It all depends on what you want to communicate….

Poorly communicated risk can have a severe effect. For instance, the news story about the risk that pregnant women are exposing their unborn child to when they drink alcohol caused stress to one of our news editors who had consumed wine moderately through her pregnancy.

 I think it’s irresponsible to say there is a risk when they actually don’t know if there is one. There is scientific uncertainty about that.
  “‘Absence of evidence is not evidence of absence.’ I hate that phrase…It’s always used in a manipulative way.” In such situations of unknown risk, there is a phrase that is often used: “Absence of evidence is not evidence of absence.” I hate that phrase. I get so angry when people use that phrase. It’s always used in a manipulative way. I say to them that it’s not evidence of absence, but if you’ve looked hard enough you’ll see that most of the time the evidence shows a very small effect, if at all.

So on the risks of drinking alcohol while being pregnant, the UK’s health authority said that as a precautionary step it’s better not to drink. That’s fair enough. This honesty is important. To say that we don’t definitely know if drinking is harmful, but to be safe we say you shouldn’t. That’s treating people as adults and allowing them to use their own judgement.

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