The problem of evidence

Stands to reason, people have better ideas and get more done when fresh than when they have been working for many hours or days on end, right? Therefore, people who work shorter weeks will be more productive. This seems so self-evident that it shouldn’t need proof. But the idea that a shorter week might be better for everyone is still a bit out-there, so therefore we need evidence for everything we say. (Even though the vast majority of actual policy is nothing to do with evidence. But that’s another story).

So a new Australian study, featured today in the Daily Telegraph, is interesting. The researchers ran some standard cognitive tests (remembering numbers backwards, that kind of thing) on a bunch of women and men who were over 40 years old, and found that those who worked 25 hours a week did the best. Test attainment dropped off a little for the 40-hour-weekers and even more for those who worked 55 hours a week. All did better than people who didn’t work at all. There was no gender difference.

This is interesting, because it coincides with common sense, and suggests that a shorter working week might be more productive because people get slower if they work longer hours…

But wait! There is a huge problem with the study. Its narrative suggests that the pattern is seen only in people over 40, and indeed this is who was tested. But the researchers didn’t test anyone under 40! It is entirely possible – nay likely – that exactly the same pattern of cognitive attainment is seen in people of all ages who work different numbers of weekly hours. It might have nothing to do with age at all.

Secondly, while common sense suggests that tiredness from long hours might reduce cognitive ability, we can’t assume this from the study, as we don’t know what caused what. Perhaps people who work more slowly (and do less well in cognitive tests) work longer hours to get the work done? Or perhaps the really smart people (who do best in cognitive tests) are smart enough to get themselves 25 hour a week jobs? Correlation is not causation, and from this study alone, we just don’t know.

I believe that a shorter working week, coupled with a living wage and affordable housing, would be better for everyone of all ages. This study shows that people who work long hours do worse in cognitive tests. But it has a long way to go before proving that older people are slower than younger ones at work, despite its claimed concluding sentence that “in middle and older age, working part time could be effective in maintaining cognitive ability”. I’m sticking with the court of common sense, until studies come along which do actually show what they claim to.

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