Is there somewhat of a study or some type of assessment on the psychological costs on the soldiers to go into combat again and the possibility to do more combat?

WHITEHOUSE: Press Briefing

But there may be an explanation: that the psychological make-up which encourages K-type behaviour worked in the past but is not appropriate to modern circumstances.

ECONOMIST: Why, as people get richer, do they have fewer children?

Psychologists investigating eudaimonic versus hedonic types of happiness over the past five to 10 years have looked at each type's unique effects on physical and psychological health.

WSJ: University of Wisconsin Study Finds Eudaimonic Happiness Lessens the 'Bite' of Risk Factors for Disease