Oh my, there really has been some bad maths from the Vote Leave campaign in a report they recently published. The graph above from page 29 of the report make a totally elementary error in its implication that migration caused the increase in A&E attendances.
A phrase every A Level stats student knows (and many who have not studied stats know too) is “correlation does not imply causation.” It is easy to find things that correlate but many of these correlations are spurious. Indeed there is website devoted to such silliness.
Just because things correlate it does not mean one causes the other. For example, as one wag on Twitter demonstrated, the increase in global average temperatures is correlated with the increase in net migration. Does that mean migration causes climate change?
Of course correlation may imply causation but before you make such a bold statement you should consider other possibilities. So, why might A&E admissions be going up? Given I’m a trade union official for UNISON, the biggest union in the NHS, I can speak with a little knowledge from talking to our members. I would theorise that perhaps the fact that we have an ageing population this would mean more A&E admissions.
Is it possible to check this theory? Well yes, it is very easy.
Here you will find A&E data that gives admissions by age group. The age related data only goes back to 2011 (unlike the data in the Vote Leave report which goes back to 2002) but it still provides enough evidence to debunk the Vote Leave claim that migration has caused the increase in A&E admissions.
I compared the data between 2011 and 2014 to see the age related breakdown. I grouped them in three age categories 0-19 (children and youths); 20 – 49 (adults); 50+ (older adults). Remember we know migrants are typically younger and nearly all under 50.
We can clearly see here the biggest increase in A&E admissions are in the 50+ age group. in fact the 50+ age group are just over 50 per cent of the increase in admissions. Given migrants are younger and nearly always well under 50 it is safe to assume that migrants are not responsible for this part of the increase.
Also, this article from the GP website Pulse says:
As many as 5.8 million people attended A&E in 2012/13 after failing to get a GP appointment, representing more than one in four of all attendances, researchers have claimed.
According to the table in the Vote Leave report, net migration was 177,000 in 2012. So these 5.8 million admissions are unlikely to be all down to migrants otherwise it would mean they’d each visited A&E 30 times in a year!
Remember two facts. First, migrants tend to be younger than the average age of the rest of the adult population. Second, younger people have fewer health problems and use the NHS less than older people.
Of course migrants may have contributed to increased A&E admission but it is simply ludicrous to assume (as Vote Leave have done) that migrants have caused all of the increase when it is clear this ain’t so. And to cap it all after getting a spurious correlation they then use that to extrapolate out as to what the A&E admissions increase will be in 2030. This is a woeful abuse of statistics.
What makes this misrepresentation even more egregious, is that under the graph it says “there is a very strong correlation (>0.9)” and the graph shows the R squared value (or coefficient of determination) to give some technical gravitas to demonstrate “we know what we are doing.” But they don’t know what they are doing as they have ignored the iron rule that “correlation does not imply causation.”
Either they know this and they are being wilfully misleading, or they are shooting from the hip without knowing what they are doing.
If it is the former we cannot really trust anything else they say. If it is the latter, it makes me wonder what else they don’t know what they are talking about.