The double constraints of a time limit and the group format render diagnostic homogeneous composition essential. IPT-G groups should be composed on the basis of specific criteria, such as depression or binge eating. Homogeneous composition brings common target problems that enhance motivation and facilitate the rapid emergence of a working focus for the group. This promotes early cohesion and expedites movement through the crucial early stages of group development. It creates an environment where the members feel almost immediately understood, often in contrast to their experiences in the outside world. For example, members of a binge eating group experience relief at being able to talk about details of their eating behavior that have likely been kept a carefully guarded secret. This instant sense of membership allows the group to move forward rapidly, allowing more time for advanced interactional work.
We recommend that groups begin with seven to nine members. Losing a member or two is not uncommon, but if membership drops below six it becomes increasingly difficult to maintain a strong interactive group atmosphere. Group membership should ideally be closed, with all members beginning and ending together; in reality, adding members over the first two or three sessions (only) may prove necessary. This should be minimized, as any change in membership reconfigures the group’s relationship balance and sets back the level of group work.
Group composition requires system-level thinking. As a general rule, it is useful to identify patients who may not fit into the group or may impede group progress.
Specific considerations in selecting IPT-G group members include whether an individual fully meets the purpose of the group (e.g., binge eating, major depression); a single member who is significantly older or younger than the rest; a single member of a particular gender; active suicidal ideation or an acute, severe current stress situation, which might monopolize group discussion during the early sessions and be more appropriately treated in individual IPT; inability to identify focal problem areas during assessment; a highly defended personality style, making the individual likely to intellectualize the nature of his or her own interpersonal problems, and those of others; low motivation; availability for all group session dates; and more than three members with moderate personality pathology. These considerations are not intended as absolute criteria but rather as a screening guide to alert the therapist to possible difficulties. Seasoned therapists adept at IPT may certainly be able to manage individuals who fall into some of the aforementioned categories, such as those experiencing acute distress or who are highly intellectualized, and such therapists may choose to include these individuals in group treatment. Overall, only major discrepancies across potential group members matter; minor fine-tuning of membership is generally unnecessary.