The invalid assumption that correlation implies cause is probably among the two or three most serious and common errors of human reasoning. ~ Stephen Jay Gould, evolutionary biologist and author, 1981
I have a background in science. I was trained in the scientific method and have the conscience of Karl Popper on my shoulder much of the time. In recent years I have been able to unshackle myself a little from the constraints this can place on my tolerance, and been able to stay chilled a little more than I used to be able to when I see or hear people purport to use ‘science’ to make questionable and spurious claims.
However, every now and then I get mad. Especially when the people behind the claims ought to know better. When people misuse ‘science’ to dupe the public and sway political and social debates.
This week was one of those weeks. Junior Doctors are currently in the middle of a dispute with the UK Government, which led to the first of three planned strikes. Now, I have no wish to make any party political points in this post, and my compulsion to write is not driven by any particular support for either side in the dispute. Rather it is based on the oft quoted claim made by Jeremy Hunt, the Health Secretary, that: “….at the moment we have an NHS where if you have a stroke at the weekends, you’re 20% more likely to die. That can’t be acceptable.”
Now if this bald fact were true it would clearly be quite alarming, and no doubt the public would be rightly supportive of action to do something about it. Before digging into the accuracy or otherwise of the claim, it has clearly proved to be a pretty ‘sticky’ soundbite.
As well as Hunt himself making sure it is reinforced at every opportunity, It has been repeated parrot fashion by other members of the Cabinet when asked for their views on the situation. Michael Portillo, an ex-Cabinet minister with a high profile on television as a political commentator, was heard quoting it as evidence for the need to make contract changes. When called out on it by a medical spokesperson on the BBC programme, This Week, on 14th Jan 2016, and being told that it was a serious misinterpretation of the research, Portillo said, “Well, I thought that’s what we were basing the reforms on.” Quite a chilling moment; when a senior figure such as Michael Portillo has the whole basis for a fundamental change to NHS contracts shattered beneath him, but goes on blindly wishing to believe the soundbite anyway.
The potency of the underhand tactic with the general public was evident during BBC’s Question Time programme from London on the same evening. One member of the audience, with fear written all over his face, regurgitated what he called ‘the fact’ that he stood a greater chance of dying in hospital at the weekend. “The facts are there” he said, “people are more likely to die at the weekend, because there are not enough consultants and relevant doctors in the hospital.” (note that by this stage the original specifics relating to just stroke have disappeared and the ‘fact’ has become universal). The statement has broken through into public consciousness. This is how propaganda works. Who cares about evidence. If it hits a nerve and feeds people’s most basic fears then it will stick.
The authors of the paper in question (Roberts, Thorne, Akbari, Samuel & Williams) say that the data suggests that people admitted Friday to Monday, who are looked at again 30 days after their stay, have a slightly higher statistical level of mortality. But the authors have been cautious in drawing too many sweeping conclusions, and have said it would be rash to assume that this statistical variance could be attributed to staffing.
In fact, Dave Curtis (Honorary Professor in UCL Genetics Institute) wrote an
interesting piece which looked in detail at the statistics behind the study. He reveals that admission rates for strokes are lower on the weekend than in the weekdays. Since there is no reason to believe that incidence of stroke is affected by day of the week, it might be reasonable to speculate that those that do get admitted at the weekend are more severe and therefore have higher mortality. In fact, Curtis goes on to say that he believes Jeremy Hunt is actually lying in the way he is choosing to manipulate and use the research. According to his analysis of the data presented, rather than being 20% more likely to die on the weekend if you have a stroke, you are in fact less likely to die. It may be true that of people admitted to hospital more die, but that merely reflects the increased severity of their condition.
As with all science, experimental results give rise to new questions, new lines of enquiry and raise doubts over previously held beliefs. Good science, and the knowledge it reveals, tends to build slowly, one study at a time, retesting and revalidating prior claims, altering potential variables, and being very careful not fall in to the common and seductive trap of misreading ‘correlations’ as ’causes’.
So, it is absolutely valid to say that more work should be done to investigate possible reasons for any increased mortality risk for people with stroke admitted between Friday and Monday, but it is nothing short of abuse of science to be knowingly misinterpreting the data in attempts to scare the public to serve political ends.
Very helpful post. Correlation vs. causality was drilled into me during my doctorate, and I never cease to be amazed at how often they are confused… let alone used consciously to win an argument.
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