By: Love, Keisha M., and Tamera B. Murdock.
Using data from college students from the Midwestern US, these researchers find that being from an intact biological family has a positive effect on psychological well-being after controlling for attachment to parents. Also, individuals from intact biological families tend to have more secure attachments to their parents, which is also associated with better psychological well-being.
Attachment to parents and psychological well-being: An examination of young adult college students in intact families and stepfamilies. Journal of Family Psychology 18 (4): 600-8.