Intended for healthcare professionals


Brexit: the decision of a divided country

BMJ 2016; 354 doi: (Published 06 July 2016) Cite this as: BMJ 2016;354:i3697 infographic, showing that more people from the south of the UK voted to leave the European Union

Brexit: the decision of a divided country

I’d like to thanks Christopher Hanretty and Rob Ford for their comment and, of course, they do have an interesting point to make, but I think it is one that has been over-made in recent days.

The term “size of the denominator population” is used to explain that some population groups are bigger than others, and that this really matters greatly. The attached map, which was kindly produced by Will Stahl-Timmins, shows the number of voters who were polled in each region adjusted to remove sampling bias. The proportion who voted Leave in each area is shown as an arc and these are then summed to illustrate how the absolute numbers of Leave voters was higher in the South. Geographers usually define the UK north/south divide by splitting the midlands in half.

Maps can often help clarify the importance of differing relative risks, especially when they use symbols or even projections that account for the differing size of the denominator populations. On November 28th I am giving the annual Political Studies Association Lecture on “Another World is inevitable: Mapping UK general elections - past, present and future”. I’ll try to explain more in that and also include some examples of mapping in medical journals. Future political analysis could well benefit from knowing that it is not just the highest relative risks that matter, but the overall spread of an affliction, or the causes of that affliction.

Furthermore there are often connections between politics and health that are not well known. I speculate on some here in regards to Brexit:
In the five years leading up to the Brexit vote the self-reported health of the population of the UK, across all of the UK, became much worse, year on year. This mostly effected older people. That rapid deterioration in people's health may well have had an impact on how many of those who got to vote on June 23rd felt about their lives.

Rudolf Ludwig Carl Virchow put it simply many years ago: "Medicine is a social science and politics is nothing but medicine". writ large

Competing interests: No competing interests

11 July 2016
Dorling Danny
Halford Mackinder Professor of Geography
University of Oxford
School of Geography and the Environment