I'd like to read this study or abstract, at least.
This is the problem with the news... They try to explain something in 4 lines, and ignore the fact that we cannot explain or even suggest a real cause, or even identify the effect as the effect much of the time...
There are too many variables involved in studying human behavior (+ disease + such)
Are these people happy bc they have surrounded themselves with happy people
or were they happy to begin with and so attracted other like-minded (happy people..)
I'm sure there are other possibilities as well...
confuses fiction with reality