[dhbradshaw]

People had a measure of fitness that was accessed by asking "how active / fit are you?"

Researchers had a different measure of fitness.

If the researcher's measurements are less predictive than people's estimates, one possible reason is that there's some powerful mental effect going on.

However, a more parsimonious interpretation might be that self-perceived fitness was a better measurement than the one the researchers came up with. This isn't completely unreasonable because the subjects have access to more information about their own health than do the researchers.

[tgb]

Agreed though the previous study had an intervention and so more directly supported the idea that the belief created benefits.