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Crisis of confidence

So Crisis, a UK-based charity supporting the homeless, brought out a report highlighting differences in mortality between the homeless and the UK population in general. The headlines that accompanied it made shocking reading. “Homeless people in the UK revealed to have life expectancy of just 47” from the Guardian is a typical example, highlighting the 30 year difference between that and the equivalent figure for the UK population. More on the media later.

Let me come clean and state my conclusions right from the off. There will be swearing.

Bullshit.

It’s not the life expectancy of the homelessness that’s 30 years lower than the UK average. It’s the average age at death. Now I know that that sounds like I’m splitting hairs over a trivial difference. Trust me, I’m not, as I will now explain.

Average age at death is just that. You look at all the deaths that happened in a population over a given period of time, and calculate the average age at which those deaths occurred. Relatively straightforward, but completely useless for comparing mortality between one population and another.

Why? Well, it could be telling you one of several things, and you have no way of knowing which it is. One explanation is, yes, that mortality is worse in the homeless population than in the population in general. But that (contrary to what the authors and Crisis seem to conclude) is not the only possible explanation. Another reason is that the alive homeless population could well be younger than the population in general.

If that explanation holds water, then another plausible narrative exists, other than the doom and gloom bandied about in the Crisis press release. This could well be an indicator of the success of charities such as Crisis and Shelter, and their less famous and more local equivalents, in tackling homelessness, so that those who are homeless are, to a considerable extent, getting rehoused and being helped back on their feet again. Infuriatingly, “average age at death” doesn’t tell you that, because it doesn’t take into account differences in the age-structure of the population. At all. Life expectancy does. And that’s not a trivial difference.

Consider the following question: what’s the average age of death among students? Now, I don’t know the exact figure, but I’d hazard a guess that it’s somewhere in the low 20s. Does that mean we should be getting hysterical about the 50 year gap between mortality amongst students and the UK population? Of course not. Thankfully, very few deaths occur among students. However, those that do, occur disproportionately to those in their twenties… because students are in their twenties. If you compare two populations with wildly different age-profiles, you have to account for those differences, otherwise you’re comparing apples with oranges and will draw silly conclusions.

A number of things really anger me about this study. One is that, well, in my opinion at least, every stage of this research and the chain of its dissemination failed somewhat. The researchers compared an indicator that was never ever fit for the purpose they were using it for, although they did refrain from calling it life expectancy, and did include a number of caveats explaining that perhaps “average age of death” isn’t quite as reliable an indicator as all that, and probably shouldn’t be used. But, infuriatingly, they went ahead and did it anyway, and in doing so they (probably unintentionally) set the trap. The Crisis press release took this one stage further, by continuing to avoid using the word life expectancy (good!) but removing all the caveats (arrgh!), thus priming the trap and making the bait look more attractive.

The media then snatched the bait, and went about reporting the “findings” with merry abandon. I’ve already mentioned the Guardian above, and the BBC and Telegraph‘s equivalent fervour about the shocking disparities in “life expectancy” are two more examples. One of the popular themes in these stories was comparing the figure to the life expectancy of the Democratic Republic of Congo, which the Telegraph and Guardian both did. Way to trivialise the situation in a country torn by civil war, with a per capita income of a paltry $280 a year, where malaria and pneumonia contribute to an under-5 mortality rate of a whisker under 20%. Classy, chaps, truly classy.

It gets worse. Even NHS Choices got it wrong. NHS Choices. Including the comparison to DR Congo. FFS. You should know better.┬áBut in some senses, you can’t fully blame the media. After all, a big, juicy, gossipy story was dangled in front of their noses.

But what really infuriates me is that despite all this, homelessness may still actually be a serious problem in the UK’s towns and cities, and actually, as I said before, a plausible story emerging from this data is that Crisis et al do a good job in ensuring that the homeless don’t remain so right through into old age. Some of the sub-plots that emerge in the report are on equally (if not more) dodgy ground. The narratives blaming drink and drugs as the main killers are based on data that are similarly unfit for purpose, for similar reasons. The data simply do not show that. I worry that those sub-plot conclusions are driven more by pre-conceived opinions about the habits of the homeless rather than actual data, and that they need to be challenged with proper evidence. That’s dabbling in speculation beyond my area of expertise though. I’d welcome anyone who actually knows more about that to enlighten me.

If you’re going to try and win hearts and minds, please do it with good data, fit for purpose, and construct narratives that actually describe what the data show. These kind of PR pieces may tug enough emotions to get people to part with some cash this holiday season, but do it at the expense of reinforcing prejudices and trivialising other problems. My Christmas donation this year will be to Cancer Research UK. They do a spectacular job on research into this horrific disease (or rather, very large group of diseases), often with terrific selflessness, passion and determination, and don’t resort to PR nonsense to big themselves up over Christmas (in fact they make a bloody good effort to combat it). I encourage you to do the same.

Merry Christmas.

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