Jenny Craig and how not to do a meaningful comparison

So, I heard this NPR story the other day about how Consumer Reports had rated diet plans and that, much to my surprise, Jenny Craig came out a solid winner.  Much of the story focused on the fact that the comparison relied on studies paid for by the diet plan companies themselves.   Of course, pretty much all the studies were funded by their sponsor, so that was the best comparison they could make.  And, all the studies were peer-reviewed.

Here’s the true glaring problem, though, as I learned from the Times— it’s hard to claim that someone is “on” a diet plan when that diet plan involves shelling out hundreds of dollars per month for specialized food, but instead that food is provided for free because you are part of a study.  In the real world, long-term compliance with plans is a huge factor in their efficacy, and obviously cost is going to be a meaningful part of that.  In the real world, people shell out a lot of money for Jenny Craig and drop out.  In the study, it was all free and they stayed in:

The magazine said Jenny Craig had “the edge over the other big names” on the basis of a two-year study published last year in The Journal of the American Medical Association. In that study, 92 percent of 442 overweight and obese women stuck with the program for two years, which Consumer Reports called a “remarkable level of adherence.” They lost an average of about 16 pounds.

But the magazine failed to report that the women in the study didn’t pay a dime to sign up for the Jenny Craig program. Unlike real Jenny Craig customers, they received $6,600 worth of membership fees and food during the two-year study.  [emphasis mine]…

The study wasn’t designed to test the success of Jenny Craig in the real world, but to determine whether a free prepared-meal program could help people lose weight and keep it off.

I’m really not sure what’s the point of even comparing the success of a plan that is not even intended to test “real world” use.  As for the real world of Jenny Craig:

Researchers led by the Cooper Institute in Dallas tracked 60,164 men and women enrolled in the Jenny Craig Platinum program between May 2001 and May 2002. Only 3 out of 4 dieters stuck with the program for a month; by 13 weeks, 58 percent had dropped out, and after a year the dropout rate was 93 percent. Those who stuck with the program for at least three months did lose about 8 percent of their body weight, but there is no long-term data on whether they kept it off.

The point here is not to slam Jenny Craig (though I have seriously been considering weight watchers on-line of late– a friend has had some good success), but rather to suggest that the Consumer Reports conclusion is totally unfounded.

About Steve Greene
Professor of Political Science at NC State

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