Lack of confounding variables
There are many orphan studies before the Romanian orphan study was published
IE: orphans studies during WW2
These children had varying degrees of trauma which means is difficult to disentangle neglect, physical abuse etc from intitusionalised care
However orphans from Romanian orphanage study were given up by loving parents who could not afford to keep them
This means the results obtained were less likely to be confounded by negative early experience (high internal validity)