Between books, drugs and surgeries, weight loss in the United States is a $20-billion-per-year industry, with 108 million Americans bellying up to the weight-loss bar each year [source: ABC News]. Not surprisingly, weight loss studies -- good, bad or ugly -- get a lot of press in the U.S.
Take the popular idea that eating breakfast beats obesity, a sugar-frosted nugget derived from two main studies: One, a 1992 Vanderbilt University randomized controlled study, showed that reversing normal breakfast habits, whether by eating or not eating, correlated with weight loss; the other, a 2002 observational study by the National Weight Control Registry, correlated breakfast-eating with successful weight-losers -- which is not the same as correlating it with weight loss [sources: Brown et al.; O'Connor; Schlundt et al.; Wyatt et al.].
Unfortunately, the NWCR study failed to control for other factors -- or, indeed, establish any causal connection from its correlation. For example, a person who wants to lose weight might work out more, or eat breakfast, or go whole-hog protein, but without an experimental design capable of dialing in causal links, such behaviors amount to nothing more than commonly co-occurring characteristics [sources: Brown et al.; O'Connor].
A similar problem plagues the numerous studies linking family dinners with a decreased risk of drug addiction for teens. Although attractive for their simple, appealing strategy, these studies frequently fail to control for related factors, such as strong family connections or deep parental involvement in a child's life [source: Bialik].