Tuesday, 18 May 2010

Parents have more sense than BBC journalists, then

From the BBC, another reprint-the-press-release article, this time with the headline Parents 'more worried about murder than obesity' threat.

On the whole, this seems like a sensible balance. Murder may be rarer than "obesity" but the consequences are significantly more severe.

The findings, in a YouGov poll of 1,244 parents, contrast with data showing the risk of a child being killed by a stranger is a million to one.

The risk of severe health problems for children due to lack of exercise is one in three, figures have suggested.

"Figures have suggested". No mention of what figures, or how reliable, or anything. Also note the addition of the qualifier "by a stranger", which is necessary given that the risk of being killed - at any age - by someone one knows is considerably higher.

As mentioned before, research shows that - for Western industrialised populations at least - the death rate is not significantly correlated with weight (and in so far as it is, the government-mandated weight is correlated with a higher risk of death within a particular time period than heavier weights).

The article does talk more about "long-term health problems" than death as a consequence of obesity, but what's not mentioned is that the evidence that the correlation is causative is sparse. Indeed, for many "obesity-related" conditions, there is more evidence of the reverse - that weight gain is either a symptom of an underlying condition or caused by an underlying factor that also causes susceptibility to that condition.

That lack of evidence of causation is of course a serious problem for the government policies developed around this. It's much like the government, upon discovering that people with blonde hair were more likely to have a particular health condition, recommending hair dye - except that in this case some of the suggestions for hiding the symptom are actively harmful to health.

The article doesn't, at least, mention restrictive diets for children as a possible "solution", instead advocating more exercise and walking to school. The problems with "more exercise" and "walking to school" as a solution have been repeatedly said elsewhere, so to summarise:

  • Not every child can exercise that much, because of disabilities, and/or a lack of suitable or sufficiently cheap places to exercise near where they live, and/or a lack of free time.
  • Similarly, it's not practical for every child to walk to their primary school, due to the distance, or lack of time, or inaccessible routes.
  • The effects of exercise on weight are not particularly clear in adults. I don't know if there have been useful studies specifically for children.

So that's the conclusions, but what about the data used to conclude them? Going back to the article, it's fairly clear that - despite YouGov being a reputable survey company - the questions that they were given to ask were clearly set with the aim of producing the press release in mind. From the BBC article.

But only one in 20 picked concerns about poor health in later life due to the child's levels of physical activity.

Here's the options for the question, which was "which of these do you fear most for your child?"

  • They are injured or killed in a road traffic accident - 30%
  • They are abducted or murdered - 30%
  • Poor health in later life due to your child's current levels of physical activity - 5%
  • None of these - 21%
  • Don't know - 7%
  • Prefer not to say - 7%

This is not a good question.

Note that the survey - unlike the press release and the article - doesn't qualify "abducted or murdered" with "by a stranger". Given how prevalent abusive relationships are, that makes the "million to one" statistic pretty much irrelevant. It's like asking someone whether they're scared of being bitten, and then laughing at them if they say "yes" on the grounds that hardly anyone is attacked by sharks.

The important thing to note is that the survey only gives those three options, plus a few standard "none" options. If the survey was repeated, but with a more substantial list of plausible fears (and perhaps some that the surveyors believed less plausible), then this would give a very different result. People tend to go more for options that they're prompted for, rather than "Other". Of the three options, especially as worded, the third is - regardless of relative risk - considerably less scary.

It wouldn't surprise me if they wrote most of this press release before the survey results were back, and just added the exact numbers later.

So, bad data collection, and then conclusions that aren't really supported by the data anyway, and then reprinted pretty much from the press release without any challenge. Exactly the "standards" I've come to expect from science reporting, in fact.