Why is it thought that left-handers live less long? Chris McManus University College London Statistical Fallacies in Research & the Media Royal Statistical Society 1 st June 2015

Dear Emily, David and Chris, very much looking forward to your talks at the RSS event on 1st June in London. We now need to start finalising the details of the event, and for that I need titles and abstracts. I sketch out below a draft schedule and suggested some ideas for titles and topics based on previous discussions. Please could you let me know what you think to the schedule and send me some further details of your talk (Emily, if you are happy with your talk as previously discussed then no need to supply further info). Many thanks, Gwilym Statistical Fallacies in Research & the Media: RSS, Erroll Street, London, 1st June pm Intro from the Chair (Prof Gwilym Pryce) 5.05pm Role of Statistics in Society & the Media (Dr Emily Grossman) Statistics too important to leave to the experts: the need to raise statistical literacy and media awareness Source of statistical fallacies perpetuated by the media: Sometimes arise because of genuine errors made by experts. Sometimes emerge because of the way information is passed on and used in the media. Sometimes errors are perpetuated because the media knowingly distort statistics to make a good story. Emily illustrate with examples from her own work as an educator and broadcaster 5.35pm [Title: e.g. "Left handed people die young"] (Chris McManus) Importance of understanding social context in statistical research Academic origins of the left-handed people die young fallacy -- details of the papers and data used in articles published leading journals Social context of the data affects how we interpret it -- under-reporting of left-handedness led to the misinterpretation of data Other examples of this and related fallacies 6.10 [Title: e.g. "The Improbability Principle" ] (Prof David Hand) 6.45pm Q&A 7.00pm

Why is it thought that left-handers live less long? A recurring story on the internet and elsewhere is that left-handers die younger. Or as one website charmingly put it, those “born with this crippling condition … die sooner”. Another said, “Left-handed people seemingly die 6 to 9 years sooner than right-handed people. No one has a good explanation for why”. It isn’t true, but beneath the myth is a statistical fallacy which is surprisingly prevalent. Part of the problem is that left-handers do indeed die at a younger age but despite that do not live less long. right-handed-people-No-one-has-a-good-explanation-for-why-ab572-0

And the other four reasons? That can wait until later…

Stanley Coren and Diane Halpern, 1988, Nature, “Do right-handers live longer?”

“[a]bout 2 per cent more right-handers than left- handers survive at each age (p<.001) (see figure)”.

Is this difficult to interpret? t-test, t=0.62, 1706 df, p=0.537 Diff= 35 weeks

Nature, 16 th June 1988 Several letters, but none on the statistics…

Nature, 18 th April 1991

New England Journal of Medicine, April 4 th, 1991

New England Journal of Medicine, Oct 3 rd, 1991

Handedness evaluated in 1976 or 1978; followed up in 1988

Ken Rothman, Epidemiologist

The problem with the Halpern and Coren study. They knew the ages of – dead right-handers, and – dead left-handers But, they did not know the ages of – living right-handers and – living left-handers If living left-handers are also younger than living right- handers – Secular trend – But no effect on survival Halpern and Coren’s study was a ‘death cohort study’ – Death cohorts always confound secular trends and age at death – ‘Birth cohort studies’ do not suffer from that problem.

Are there secular trends in handedness?

Secular trends

Sex differences

Combining all the nineteenth century data

So is this problem only found in studies of handedness?

Err, No…! Lancet, 1994

BMJ, 1996, Christmas edition

Finally, we committed a statistical howler in our Christmas issue. We published a paper that concluded from obituary data that doctors from the Indian subcontinent and anaesthetists died young. Chris McManus suggests that the same data might have shown that doctors who had Oasis CDs or who were called Tracy or Kevin also died young (p 1132). It's a problem of denominators. There were none in the paper, and the seemingly increased risk of doctors from the Indian subcontinent and anaesthetists of dying young is probably because the population from which they come is young. Many people wrote to point out the error. We are comforted by the Lancet having made the same mistake two years ago.

Finally, we committed a statistical howler in our Christmas issue. We published a paper that concluded from obituary data that doctors from the Indian subcontinent and anaesthetists died young. Chris McManus suggests that the same data might have shown that doctors who had Oasis CDs or who were called Tracy or Kevin also died young (p 1132). It's a problem of denominators. There were none in the paper, and the seemingly increased risk of doctors from the Indian subcontinent and anaesthetists of dying young is probably because the population from which they come is young. Many people wrote to point out the error. We are comforted by the Lancet having made the same mistake two years ago.

Finally, we committed a statistical howler in our Christmas issue. We published a paper that concluded from obituary data that doctors from the Indian subcontinent and anaesthetists died young. Chris McManus suggests that the same data might have shown that doctors who had Oasis CDs or who were called Tracy or Kevin also died young (p 1132). It's a problem of denominators. There were none in the paper, and the seemingly increased risk of doctors from the Indian subcontinent and anaesthetists of dying young is probably because the population from which they come is young. Many people wrote to point out the error. We are comforted by the Lancet having made the same mistake two years ago.

Finally, we committed a statistical howler in our Christmas issue. We published a paper that concluded from obituary data that doctors from the Indian subcontinent and anaesthetists died young. Chris McManus suggests that the same data might have shown that doctors who had Oasis CDs or who were called Tracy or Kevin also died young (p 1132). It's a problem of denominators. There were none in the paper, and the seemingly increased risk of doctors from the Indian subcontinent and anaesthetists of dying young is probably because the population from which they come is young. Many people wrote to point out the error. We are comforted by the Lancet having made the same mistake two years ago.

Finally, we committed a statistical howler in our Christmas issue. We published a paper that concluded from obituary data that doctors from the Indian subcontinent and anaesthetists died young. Chris McManus suggests that the same data might have shown that doctors who had Oasis CDs or who were called Tracy or Kevin also died young (p 1132). It's a problem of denominators. There were none in the paper, and the seemingly increased risk of doctors from the Indian subcontinent and anaesthetists of dying young is probably because the population from which they come is young. Many people wrote to point out the error. We are comforted by the Lancet having made the same mistake two years ago.

And yet still they keep coming…

This is clearly a modern myth (and there seems to be no sign of it before 1988). So why is it so prevalent and so resistant to evidence?

#4: They’re more likely to go insane #3: They’re screwed at school #2: They’re more easily scared… #1: Hating them is ingrained in our culture So what were the other four reasons?