A study of 86 patients, all of whom suffered from disease T and received the same standard medical treatment, divided the patients into 2 equal groups  One group' s members all attended weekly support group meetings, but no one from the other group attended support group meetings  After 10 years, 41 patients from each group had died
Clearly, support group meetings do not help patients with disease T live longer
The members of the group that attended weekly support group meetings lived 2 years longer, on average, than the members of the other group.