Ever since Group Therapy became established as a scientific method for the furtherance of mental health, therapists have looked for ways of measuring the behaviour of the Group. It is clear, for example, that there are important differences in structure between a group of people newly assembled in a railway carriage and those who share the same dining table at the end of a long sea voyage. Interpersonal relations have been established in the latter company, and each member has himself achieved some kind of relationship to the group as a whole. It cannot be conceded that any purpose would be served in quantitatively measuring these relationships in the two kinds of groups which have been mentioned. This is because they are accidentally formed groups, lacking a basic purpose and without a pre-appointed leader. Membership of such a group may be interesting, boring or entertaining, but it cannot be said to play any great part in the life-plan of the individual.