That has not stopped them from rounding up the usual suspects. A study in the September issue of the American Journal of Public Health, for instance, warns about fast food "clustering" near schools. "The concentration of fast-food restaurants around schools within a short walking distance for students is an important public health concern," the researchers declare, "in that it represents a deleterious influence in the food environment that may undermine public health efforts to improve nutritional behaviors in young people."

 Since "public health" appears twice in a sentence that also mentions the environment, this must be serious. But what exactly are they talking about?

 The study found that 80 percent of primary and secondary schools in Chicago are located within 800 meters of a fast-food outlet (about a 10-minute walk) and 35 percent are only 400 meters away. "A significantly greater number of fast-food restaurants are located within a short distance from schools than would be expected if there were no spatial dependence," the authors report.

 Although the Center for Science in the Public Interest immediately cited the study as evidence that the "food industry targets children," the simplest explanation is that fast food restaurants tend to be located in commercial areas with many potential customers. There was no sign of "clustering" around schools in noncommercial areas.

 In any case, the researchers present no evidence that having a McDonald's or Subway near school makes students fatter. They nevertheless close their article by suggesting fast-food-free zones around schools that would "remove noxious elements in the food environments that schoolchildren are exposed to every day" -- and, incidentally, limit the lunch options of all the adults who happen to work or shop nearby.

 This is the sort of policy -- coercive, choice-restricting, and almost certainly ineffective -- that comes from treating behavior like a contagious disease.