Why is it thought
that left-handers
live less long?
Chris McManus
University College London
Statistical Fallacies in Research & the Media
Royal Statistical Society
1st June 2015
• 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 lefthanders survive at each age (p<.001) (see figure)”.
t-test, t=0.62, 1706 df, p=0.537
Diff= 35 weeks
Is this difficult to interpret?
Several letters,
but none on the
statistics…
Nature, 16th June 1988
Nature, 18th April 1991
Nature, 18th April 1991
New England Journal of Medicine, April 4th, 1991
New England Journal of Medicine, Oct 3rd , 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 righthanders
– 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?
1
6
%
Secular
trends
1
4
%
F
e
m
a
l
e
s
1
2
%
M
a
l
e
s
1
0
%
8
%
6
%
4
%
2
%
0
%
1
9
0
0
1
9
1
0
1
9
2
0
1
9
3
0
1
9
4
0
1
9
5
0
1
9
6
0
1
9
7
0
Y
e
a
r
o
f
B
i
r
t
h
G
i
l
b
e
r
t
&
W
y
s
o
c
k
i
(
1
9
9
2
)
N
e
u
r
o
p
s
y
c
h
o
l
o
g
i
a
,
3
0
:
6
0
1
8
0
%
Sex2
differences
F
e
m
a
l
e
s
M
a
l
e
s
1
0
%
9
%
8
%
7
%
6
%
5
%
4
%
3
%
2
%
1
9
0
0
1
9
1
0
1
9
2
0
1
9
3
0
1
9
4
0
1
9
5
0
1
9
6
0
1
9
7
0
Y
e
a
r
o
f
B
i
r
t
h
G
i
l
b
e
r
t
&
W
y
s
o
c
k
i
(
1
9
9
2
)
N
e
u
r
o
p
s
y
c
h
o
l
o
g
i
a
,
3
0
:
6
0
1
8
Combining all the nineteenth century data
20%
10%
9%
8%
7%
6%
5%
4%
3%
2%
1%
1760 1780 1800 1820 1840 1860 1880 1900 1920 1940 1960 1980 2000
So is this problem only found in
studies of handedness?
Lancet, 1994
Err, No…!
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?
• So what were the other four reasons?
• #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