It is possible that mothers who spend more time with their children are generally of a higher socioeconomic status. For example, they might not have a job to go to. This would strongly influence the child later in life - for example where they grow up, what school they go to, and what types of attachments their peers experienced (and thus the behavior of those in their age group). If true, this would change the indepedent variable from attachment style to the more influential variable, socioeconomic status.
