Saturday, November 03, 2007

Back On The Menu

The Major was highly distressed by this week's report telling him to give up bacon butties- one of the few pleasures left, life not worth living, etc, etc.

I tried explaining to him that the grandly named World Cancer Research Fund is really just another pressure group, based in a flat above a Harley Street chip shop. And that their new "research" is nothing more than a highly selective trawl through previous studies. But he refused to be consoled.

Maybe he'll find this excellent Times article more convincing. It nails some major inadequacies in the WCRF's report:
  • Selection bias- "It was highly selective, boiling down 500,000 papers to the final 7,000 that were used to draw conclusions. So while it was a useful distillation of the literature, it was no more than that. Another group might have chosen a different 7,000 papers, and reached different conclusions".

  • Recall bias- Many of the selected 7,000 papers were "0rdinary case-control studies" which "rely on participants looking back and remembering how they ate and how they lived years before they developed their disease. People’s memories are poor, and are often influenced by what they think they ought to say."

  • Misclassification bias- "In case-control studies of smoking or drinking, for example, people who claim to be nonsmokers or nondrinkers may in fact be ex-smokers or ex-drinkers, whose health was damaged before they gave up."

  • False association- " For example, in observational studies people who take vitamin pills appear to suffer less cancer and heart disease, but in double-blind trials, this benefit disappears. Why? Probably because vitamin-taking is simply a marker for people who are health-conscious generally. The benefit comes from some other aspect of their behaviour which cannot be adequately corrected for."

  • Statistics- "A result can claim to be statistically significant if the odds of it arising by chance are one in 20. Those are not especially long odds, so plenty of spurious results get published."


Take half a pound of crisply grilled bacon (smoked), two slices of thick cut Mothers Pride, a generous dollop of butter, and a lengthy squirt of Heinz Ketchup.


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