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Exercise can cancel out the booze? Association ≠ causation

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It has been suggested to us that we offer a weekly “Association ≠ causation” feature.  Not sure we can promise weekly delivery, but we’ve certainly written on this theme a lot in 10 years.  And here’s the latest installment.

CNN reports: “Exercise can cancel out the booze, says study.”

No, it did not. What the study, in the British Journal of Sports Medicine, stated was “We found a direct association between alcohol consumption and cancer mortality risk.”  And – repeat after me –  association ≠ causation.  So a statement of causation – such as “exercise can cancel out the booze” – is an overstatement.

OBSERVATIONAL-STUDIES-298x300Read our toolkit primer, “Observational Studies – Does The Language Fit The Evidence? – Association Versus Causation.”

The journal – and the authors – cannot be absolved of all responsibility for misleading statements, since their conclusion read: “Meeting the current physical activity public health recommendations offsets some of the cancer and all-cause mortality risk associated with alcohol drinking.”   The term “offsets…risk” implies causality.

But, in the end, we’re reviewing the journalism.  And if you’re going to cover studies, you need to independently vet the evidence, and what researchers claim.  And that didn’t happen here.

Not when CNN went on to report:

  • “You might want to chase that next beer with a little exercise.”
  • “Exercising the recommended amount “cancels out” the higher risk of cancer death brought about by drinking.”
  • “Similarly, physical activity lessened any greater risk of death resulting from any cause due to alcohol.”
  • They allowed the researcher to discuss a “moderating effect of physical activity” when, in fact, cause and effect had not been proven.
  • They did throw in, 3/4 of the way into the story, an independent expert’s comment that “Because it is an observational study, the results only “suggest a relationship” between exercise, drinking and health benefits.” Too little, too late, after rampant use of causal language was embedded in readers’ minds by then.

CNN wasn’t alone in this.

Even the news release sent out by the journal’s publishing company stated: “This is an observational study so no firm conclusions can be drawn about cause and effect, and the researchers acknowledge that they didn’t measure drinking patterns or dietary factors, both of which could have affected the results.”

In summary, observational research can make important contributions to public health recommendations.  But those who communicate to the public about observational data should not make it what it is not.  It is quite easy to make clear statements about the limitations of such data, as we have consistently shown.  It is a matter of choice:  do you want to hype and mislead….or do you want to educate?

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