15 August 2020 | New Scientist | 49>Who were the Neanderthals?
Paleolithic archaeologist Rebecca Wragg Sykes will be entering the
world of our mysterious cousins in an online event on 27 August.
Details on all events at newscientist.com/eventsMICROST
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UB/ISTOCK
PHOTOand after that there's no sort of control over
him. By the time he was arrested, he was
murdering people at a huge rate, quite
extraordinary. We don’t know why: he never
spoke, and then committed suicide in prison.
So this data just generates more questions.
What was Shipman doing? What system was
he using? How was he killing people? The
general practitioner Richard Baker went and
looked at all the death certificates that
Shipman had signed, and those his colleagues
had as well. It was a massive data collection
exercise, but the analysis was completely
trivial. It hits you between the eyes. The times
of day when his colleagues’ patients had died
were spread pretty uniformly over 24 hours,
but Shipman’s victims were dying around two
or three in the afternoon. We think that is
when he did home visits, visiting elderly
people on their own and giving them a huge
dose of morphine. They would die in front of
him peacefully. It’s chilling.
Again, it generates more questions. All the
families wanted to know, could he have been
caught earlier? Now this is tricky. Those of
you who have suffered statistics courses will
know that to test a hypothesis, you have to set
up a null hypothesis. A null hypothesis is
boring: in this case, that there’s nothing
wrong with Shipman at all. How soon could
we have rejected that hypothesis – how soon
could we have detected something strange
was going on?
So you work out how many deaths you
expected to occur over time with different sex
and age groups if things were normal. You can
compare that with the observed number,
subtract the one from the other and you get
excess mortality. The reality is a bit more
complex and you actually use a slightly
different statistical measure. But in Shipman’s
case you can say that, based on female deaths
alone, by 1985, after only about 40 deaths, we
could have been very confident something
was strange. Of course nobody did do that at
the time; it was no one's job to do that.
The other interesting thing is that when
they tried this method out on 1000 other
doctors around the country, they found a few
who were even worse than Shipman. It turned
out that these were enormously generous and
responsible, kind, caring doctors, who were
just living in places with a lot of elderly people
and allowing them to die peacefully at home.
That’s the difference between correlation and
causation: we could conclude that these
doctors are statistically odd, but not why. We
have to be enormously cautious. That data
does not speak for itself.Shipman's victims
A statistical analysis of the age and sex of mass murderer
Harold Shipman's victims gives clues as to his methods
● Women ● Men
1985
YearAge^ of^ victim1975 19804050607080901990 1995
SOURCE: DAVID SPIEGELHALTER