Science Can You Catch Obesity?
posted by July 26 at 13:55 PMon
… the lay press article Dan linked to says so. Well, let’s look at the key figure from the peer-reviewed scientific article in the New England Journal of Medicine.
The horizontal black lines are the 95% confidence intervals; for a given row, if the black line doesn’t touch the vertical zero line, there is a 95% chance of correlation. Reading down the figure, you have an increased chance of being obese if your mutual friends (you both agree you are friends), same-sex friends, spouse, or sibling (particularly same-sex sibling) are obese. The connections between obesity in friends and family seem to be about equally strong. Nifty.
Does this mean you become obese because of your family or friends? Let’s ask my friend David what he thinks:
All reasonings concerning matter of fact seem to be founded on the relation of cause and effect. (David Hume, 1737)(This quote is more fun if you imagine it being said with a deep Scottish brogue.)
Thanks David! The correlation between obese people having obese family and friends doesn’t automatically mean that having such relationships causes obesity. There are any number of ways this could be interpreted; perhaps obese people feel more comfortable being friends with other obese people. A study of cause and effect would be very different than this one—take skinny people and give them only obese friends, take obese people and give them only skinny friends, wait twenty years, and weigh (for example.) If you want to show a causal link between having obese friends and becoming obese, you’ll have to do that. A retrospective study like this one can’t cut it.
The authors of the article go on about how this study “suggests that obesity may spread in social networks…” but until some cause and effect studies are done, suggests does not equal proves. Claiming that this study proves obesity spreads through friends makes both David and me cranky.