Bowlby felt certain his understanding was key to a more progressive model, but at the time, nearly all research was quantitative. Today qualitative research studies are met with respect that did not exist in Bowlby’s time. The dilemma was in rating such qualities as abusiveness, unkindness, and mistreatment, even when these were acknowledged by the psychoanalytic community. Bowlby was sure that, beyond actual abuse or cruelty, unresponsive or manipulative parenting styles contributed to later mental health problems in individuals.
It was for these reasons that Bowlby is best known for his studies and theories of attachment based on early parent-child separation. It was not that attachment theory captured his interest more than other broad areas of early development, but parent-child separation could be easily documented and was less open to interpretation or misunderstanding than, for example, determining what constitutes unresponsive maternal behavior.