MPH Master pieces

Validating a fitness questionnaire

Don't worry too much about the detail, but here's a nice illustration of the effort needed to prove that a simple questionnaire is valid (does what it says in the title) and reliable (gives the same answer each time). Here is the questionnaire; here is the validation and reliability study.

Physical activity in 7-year olds

Here is a good workaday paper from a cohort study. Accurate measurement of physical activity with accelerometers and impressive rates of compliance. A nice distinction between being sedentary and not being physically active. The actual results perhaps not surprising, except that there is no social class gradient in physical activity at this age - perhaps you just can't stop children racketing around.

Don't drop dead!

Modify your risk of sudden cardiac death - don't smoke (obviously); BMI between 21 and 25; eat a Mediterranean diet (veg, grain,nuts, fish and daily alcohol); and exercise 30 minutes each day at 3 - 6 METs. At least if you are a nurse. 

Here is the study - worth a careful read. I think its main value is to show just how much depends on lifestyle. What would be your guess on how much your chances of a heart attack decrease if you keep to the four rules above? Though admittedly the diet and (even more so) the exercise rules are quite tough. 

Notice how each variable was measured. Also notice that of the 120 000 nurses in the cohort only 80 000 are included in the study, mostly because of non-completion of the diet questionnaire. I'm not sure why they focussed on sudden death rather than all death from cardiovascular disease. 

Exercise: a meta-analysis

I don't normally like meta-analysis because it is so difficult to get a feel for the individual studies  - I worry about garbage in garbage out even if the analysts have applied quality scores. But Today I make an exception: I need to see the wood for the trees. There have been many small studies which tried to get people to exercise more.

Enough metaphors for now. Here is the meta-analysis.Over 350 studies were included (like I say, there have been a lot of them); the authors paid particular attention to heterogeneity i.e. the studies and their results were all different. One key to this is use of the "random effects" model.

Difficult to summarise all those studies but looking at the first and third quartiles of the studies, most were aimed at middle aged women (40 - 50 years old), and consisted of one-hour group sessions, with between 16 and 48 sessions. Overall the answer seems to be that you can increase physical activity, by about 500 extra steps per day - I guess we'd call this modest but useful.

Various other points of interest - using fancy models such as social cognitive theory or the transtheoretical model seemed to make things worse; goal setting, rewards and other behaivoural strategies made things better. The actual amount of exercise during the programme seemed irrelevant:

"Neither the number of intervention strategies
nor the total minutes of intervention content
(including total minutes of supervised physical
activity) was associated with physical activity
outcomes."

This may fit with the theory that self-identity is important to behvaiour change: if you start to think of yourself as 'an exerciser' you will take more exercise; so perhaps participating in a programme achieves that switch in self identity?

Playgrounds

I like this study of playgrounds. Fairly simple stuff - renovate a playground and see if kids use it more. It seems there is an accepted way to measure this: the "System for Observing Play and Leisure Activity in Youth".

 

Physical activity and weight gain

How much exercise should you take per week? Lots of different answers to that.

First of all, is the aim (a) muscle strength e.g. to climb stairs or carry shopping (b) cardiovascular benefit and/or lower mortality or (c) prevent weight gain? Fifteen minutes per day may suffice for (a); perhaps 20 minutes three times per week for (b) and something else for (c)??

Secondly, we should specify the type of exercise (aerobic or isotonic) and its intensity as well as its duration.

Here is a paper directed at the connection between physical activity and weight. It's an observational study, following up middle aged women who took part in a large prevention trial. Most women put on weight as they get older (at least in the USA). The ones who didn't were spending 60 minutes per day on moderate intensity activity. That's a LOT of time.

What counted as moderate intensity? The strict definition was 21 MET hours per week (MET = metabolic equivalent), assessed by a reasonably well validated questionnaire. The paper gives details of the validity of this measure.

One interesting feature of the results is that over the 13 years of follow up, more women were in the active group. Not clear if this is a secular trend or the benefit of more time for exercise in retirement.

You may also feel that the authors take a rather strict view of weight gain - 2.3kg doesn't seem much. But they argue that 2.3kg is enough for detectable health detriment. 

Exercise - a school programme that works!

So it looks as though the UK won't hit its target for target for reducing teenage pregnancy. Changing behaviour is always difficult. Was the effort pathetic in relation to the challenge? Or did we simply lack the knowledge of what to do?

Against this background here is a superb piece of research on physical activity from Switzerland. (But why has it taken 3 years to get it into print?) Note the programme fidelity - a carefully designed intervention, well delivered. Note also the accurate measurement of outcome, including skinfold measurement for obesity, not just weight; and accelerometer measurement of activity not just at school, but also at home afterwards.

I'm also interested in the results for the younger children (7 year olds). Research in Exeter seemed to suggest that young children charge around more or less regardless of what you do - if they don't get enough exercise in school, energy fizzes out of them at home.

The VERB campaign

The VERB campaign ran in the USA from 2002 to 2006. It was aimed at 9 to 13 year olds, and sold the proposition that physical activity is fun, easy and sociable. So this was social marketing on a grand scale. Total funding was $339m.

Here is the evaluation, done by telephone survey. The basics of campaign coverage and recall seem good, but the effects on physical activity are, to say the least, modest.

On the other hand this was a nation-wide campaign. How would you react if someone came to you and said 'Could we have another $300m to run the campaign again?' You'd need some health economics. People who exercise more are healthier and live longer: scale up this small benefit in children, throw in a brave assumption or two about whether increased activity in childhood persists into adult life, and then see how much health gain our $300m is buying.