Source: https://www.researchgate.net/profile/Gary-Reker/publication/266261413_Le_Bonheur_au_cours_de_la_vie_Happiness_through_the_life_cycle/links/542b9b4c0cf27e39fa918a04/Le-Bonheur-au-cours-de-la-vie-Happiness-through-the-life-cycle.pdf