My reference class was "traits I would want in a friend". I don't really care about how often my friends feel the need to be alone.

Extroversion is probably correlated with happiness - but then again, if we accept introversion-extroversion as intrinsic personality traits, who is to say that a lonely, socially awkard extrovert won't give the same test results as a sad introvert? Correlation(extroversion, income) supposedly has a inverse U shaped curve.

Actually, the truth is I don't pick friends based on raw happiness either...it was shorthand for general emotional maturity. I wouldn't want to be less friends with someone if they were depressed, for example - it's just that I don't want anger, anxiety, insecurity, and other sorts of aggression directed at me, and people who frequently experience negative emotions are more likely to direct aggression at others.