I have been researching SPD lately and what I have been reading is that not only is it hard for a therapist to diagnose SPD but even the patient won't believe they are schizoid. It has something to do with fact that the schizoid has a rich inner world they don't let others in on, but often times when it comes to dealing with other people they are able to act normal. It is, however, just an act. The schizoid person is said to be able to fake any personality they want, but they never really are that it is just an act as are their interest in others. The schizoid isn't always a loner like some think, some don't like being lonely so they may develop "close" relationships with a person but they are superficial because the schizoid person never fully discloses their true self. So you could say they use others simply to fill that void, many schizoids would love to have a deep and meaningful relationship but it is elusive because the other people never seem to be able feel like they truly know the schizoid person the way they believe the schizoid person knows them. The schizoid person is just not interested in getting emotional with other people. In a way they mimic others, so if they are expected to show interest or empathy they show it, but they don't truly feel it. The schizoid person realm doesn't need people though, not like others if anyone can live as a hermit it is a schizoid.