A story caught my eye earlier today – it was entitled “Boost Mental Health – Do Housework” and was based on a study published in the British Journal of Sports Medicine. This is the news story and here is the abstract of the study, titled “Dose response relationship between physical activity and mental health: The Scottish Health Survey”. The strongest effect was actually for sport rather than housework, but never mind – I reckon housework makes for a better headline. What’s good about this study is that the message is less likely to be perverted by salesmen in the way that any study claiming health benefits from food or food components would instantly attract nutritionists and food supplement companies eager to cash in. Unless gyms start puffing the study to attract members I suppose. The physical activity in the study was self-reported and the problems with self-reported data have been discussed in several places. Apparently, subjects tend to report what they believe the researcher expects to see, or report what reflects positively on their own abilities, knowledge, beliefs, or opinions. Another concern about such data centers on whether subjects are able to accurately recall past behaviors.  If I were asked about my physical activity I might exaggerate the amount of exercise I take (and I may well understate the amount of alcohol I drink if my doctor asked me) and to me this seemed the most obvious danger of the self-reported element of this study, but if most people exaggerated the amount of exercise they took to more-or-less the same extent then I guess the results would not be that badly distorted. Also, there were 19,842 participants and “statistical theory tells us that the reliability of observations is proportional to the square root of their number. The more observations there are, the more random influences there will be. Statistical theory holds that the more random errors there are, the more they are likely to cancel one another and produce a normal distribution” .
This is good – it looks as if there is something relatively safe [unless you rick your back doing the hoovering, or break a rib playing five-a-side] that we can do to reduce the risk of psychological distress. And as an added bonus, our homes will be cleaner and we might see side-benefits in our general fitness. But who didn’t already know that was beneficial for them? There are an awful lot of people out there who know that exercise good for them, yet they don’t take it. They might take other things – like dubious remedies that cost them money yet have no known benefits. And they would probably go on buying the pills and forgoing the exercise if the facts were explained to them. Very often, the easier option is not the right option – but it is nonetheless the one we choose. So we spend our money on junk remedies like homeopathic pills and potions and ignore the basic, common-sense advice to eat a healthy balanced diet, exercise, drink only in moderation and refrain from smoking because it doesn’t fit it with the way we want to live – it seems that us lazy fat smokers with terrible fat-, sugar- and alcohol-filled diets are only interested in taking advice if it comes from someone humiliating us on television. I think You are What You Eat and Fat Camp are the programmes I had in mind. It’s just a shame that we don’t listen to more sensible advice. From, say Diabetes UK or The British Dietetic Association [EDIT: or the DoH, or our GPs…]
 Cook and Campbell (1979)
 Deese (1972)
 The Cook & Campbell and Deese quotes came from this page.
Edited to add: Spotted via Ben Goldacre’s miniblog, the following recent NY Times-hosted blog post is on the perils of Self Reporting. [Also discussed on the Bad Science Forums]. Technorati Profile.