Because of their efficiency and ability to keep many other factors constant, twin studies have a special appeal for investigators. Just as with any teaching dataset, a "matched-sets" dataset used to illustrate a statistical model should be compelling, still relevant, and valid. Indeed, such a "model dataset" should meet the…

National average happiness and the difference in happiness between women and men are positively correlated in European countries. This study focuses on this cross-country relationship and tests (1) whether, after controlling for socio-economic factors, the correlation is attributed to their direct relationship, or, alternatively, explained by the…