It is important to understand what unit of treatment means.  Most often, because our society has become privy to much of what therapy is about, they will self diagnose who needs therapy.  What they don’t understand is the dynamics behind the problems, which is what a therapist is to know, and they do not really know who should get treatment and who should not be included.  The “unit of treatment” means, who should be in the office at one time. 

There are many possibilities to this question and it largely depends on what the problems are that are being addressed.  Such as, in a family, one person will show signs of distress by acting out their feelings rather than speaking them.  This can be caused by one, two or more of the family members and has much to do with the parental unit’s form of parenting and the dynamics of all family members.  In this case, the “unit of treatment”  must be the entire family so that the therapist can find the dynamic that is causing the stress.
In a couple’s situation, each partner tends to diagnose what issue the other partner has and is convinced that therapy will reveal this fact.  And it will, along with the first partner’s issues as well.  Again, in relationship, it takes two to tango, as the saying goes.  It is the dynamic of the relationship, not his truth, or her truth, but the truth, where the two truths meet, that is the problem.   In order to work with the relationship, or the third truth, both partners must be in the room and is considered the “unit of treatment”.  

It is equally true that sometimes one partner will have a “personal” issue to correct and when this happens, the “unit of treatment” will be just the individual that needs to be in the office.  This can happen during couples therapy and from time to time, that person will need to have a session or two to correct that issue that is getting in the way of the relationship or is causing that person pain if they are not in a relationship.  The “unit of treatment” then will be the individual only.

In addition to all of this, a therapist may need to have other members of a person’s life come into therapy for one session, in order to fully understand what that one individual is experiencing and to best help that one person.  This visiting person is NOT necessarily part of the unit of treatment.

In deciding the “unit of treatment”, it must be left to the therapist’s discretion and decision, to her/his expertise, as to who should be included.  It is not wise to make this decision on your own.