"It's not even necessarily the case that going outside is healthy, but that healthy people tend to go outside more." Right, that's why I used the word correlat

"It's not even necessarily the case that going outside is healthy, but that healthy people tend to go outside more." Right, that's why I used the word correlated - while it's not unreasonable to think that having an active lifestyle could cause you to be more healthy, it's pretty much a statistical necessity that the two are correlated, because being very sick precludes you from having a lifestyle like that.