Crawford, C. J.  (1994).  Parenting practices in the Basque country:  Implications of infant and childhood sleeping location for personality development.  Ethos, 22(1), 42-82.

In this study, information was gathered from 200 Basque women.  Those women who had slept for several years in the parental bedroom (until 4 or 5 years of age) demonstrated significantly stronger egos and scored higher on tests designed to measure characteristics of a healthy and mature personality.  Those who had not slept in the parental bedroom demonstrated more pathological symptoms.

In other words, those who coslept with parents turned out to be more emotionally healthy when they grew up.