Originally Posted by
Maelochs
My question remains ... were the kind of people who considered riding to work as an alternative already happier people than average, or did the cycling fundamentally change them?
It could be either of those or even other explanations. What they found was that in communities where a lot of people bike to work, people are on average happier. I don't think they could even say if it was the cyclists who accounted for it. Thus it might be an effect of the milieu that is not even directly linked to cycling. Maybe areas where people bike to work tend to have other attributes, that either create or attract happy people through some other mechanism.
This uncertainty is clearly acknowledged even in the NPR article title that says
"...But How Exactly?"