Monday 21 October 2019

An interesting papear has recenty appeared in the Journal of Epidemology and Community Health by Murray et al, entitled  Inequalities in time from stopping paid work to death: findings from the ONS Longitudinal Study, 2001 to 2011

open access version at  https://discovery.ucl.ac.uk/id/eprint/10082463/1/Murray%2020190821_JECH_R2_manuscript_CLEAN%20copy.pdf

At first sight it might appear puzzling that the bottom line of the paper is that people who had worked in less advantaged, lower skilled & lower status jobs (defined by the Registrar General's class schema, which is conceptually based on skills and status) actually lived longer after leaving the labour force than those whose jobs were of higher skill and status. To cite the paper itself:

"LS members who had worked in lower social classes lived a greater number of years after they stopped work, with more time per decreasing social class."

How to make sense of this? Actually, a similar issue was also a big puzzle for the authors of the first book that decribed the contribution of the LS to the study of health inequality. To the amazement of almost everyone involved, the earliest analysis showed no social class gradient in health, or even a hint of a reverse gradient. Did this mean that all the previous research on social class differences in health including those in the Black Report, had been biased by either artefact or selection?

And what does this have to do with Murray et al.'s paper?

To cut a long story short, it turned out that high status, high skilled jobs also benefit from less arduous working conditions. Just think about the difference between a building worker and a university lecturer. Lets say both of them start to get angina pectoris. The lecturer, first of all, will probably not be affected by narowing of her coronary arteries as soon because she does not need to do much heavy lifting, digging, or other activities that equire increaed cardiac output. And when she does start to notice, it is not too hard to keep her job if she also needs to do less of these kinds of things (moving furniture, lifting large piles of books or files...).  By the time she even notices that her cardiovascular function is declining, let alone has to give up her job, her disease is far more advanced. Contrast to the building worker whose daily work activities will cause pain earlier in the natural history of the disease, and incapacitate her (or him) more quickly. Let's say the disease process is exactly the same in them both. The building worker will not die sooner than the lecturer but will have had to give up work earlier.

In other words, it is not that the people in the less skilled, lower status jobs died later, but that they had to give up work earlier in the disease process.

This phenomenon eventually resulted in a convention when analyzing social class differences in health in longitudinal follow up such as that in the LS, to allow several years to pass to "allow selection to wear off" before comparing the death rates in the different classes. After the 1st 5 years, the sicker people in the more advantaged social positions died and the social class inequalities in mortality risk re-appeared. All subsequent papers using the LS have used this adjustment, but often explain it in a rather abbreviated way (let me know if anyone wants references). With this adjustment, the class differences in mortality look about the same as in the previous, cross sectional ("unlinked") studies from 1951 onwards.

These comments are no criticism of the JECH paper, whose objectives were to show that extending the pension age is less fair to people in more advantaged social classes. But it does show the dangers in assuming that the nominal definitions of social position need to be taken with care. The social forces at work here are not derived from status or skills but from working conditions, which, while collinear to each other, do not measure the same thing.

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