As part of their joint year project on the usefulness of therapy for sufferers of migraine, Nyashia and George have randomly allotted 18 migraine sufferers to three groups. Group 1 has six one-hour sessions of group counselling with a trainee counsellor; group 2 has six one-hour self-help sessions (not led by a facilitator; the agenda is determined by the group members themselves); and group 3 consists of migraine sufferers who would like to take part in the group therapy or self-help, but who have to wait. Nyashia and George expect that the counselling and self-help groups will rate themselves as suffering less than the waiting list control group when they rate themselves at the second time point. At the beginning of the study, sufferers rate their symptoms, over the past month, from 0 (not suffering) to 5 (terrible suffering). Fourteen weeks later, they rate their symptoms (in the past month) again. What is the appropriate nonparametric test to compare the three groups?
