BMC Public Health 2009, 9:251 http://www.biomedcentral.com/1471-2458/9/251 3. their UPS persists at least 6 months; 4. their UPS is classified as undifferentiated somatoform disorder or chronic pain disorder according to the criteria of the Structured Clinical Interview for DSM-IV Axis I Dis- orders/Patient edition (SCID-I/P) [15]. Patients are excluded when: 1. UPS is not the principal somatic disease; 2. undifferentiated somatoform disorder or chronic pain disorder is not the principal DSM-IV-TR classification; 3. handicaps like cognitive mental impairment and/or blindness impending the patient to participate in the training. To optimize the comparability between the study popula- tion and the patients with UPS in daily practice and to make generalization to daily practice possible, we have decided that having a personality disorder is not an exclu- sion criterion; this is in contrast to other treatment effect studies. We do measure personality disorder with the self- report questionnaire for DSM-IV Axis II personality disor- ders (VKP) based on the International Personality Disor- der Examination (IPDE) [16]. By measuring personality disorders using this instrument, we can not only describe the study population in terms of personality disorders, but also identify the influence of personality disorders on (cost-)effectiveness. Patients are recruited from general practices and outpa- tient clinics of general hospitals in and nearby Rotterdam, the Netherlands. Physicians' attention is drawn to the group training by periodical postcards informing them when and how they can refer patients to the group train- ing. Patients' attention is drawn to the group training by announcements in local newspapers and on websites of patients' associations, in which they are asked to make an appointment with their physician to discuss referral when interested. Physicians decide whether the physical symp- toms are medically explained or unexplained hereby checking the first exclusion criterion, after which they refer patients when they find this appropriate. After refer- ral, patients are invited for an interview, preferably in a medical setting, in which they are verbally and in writing informed about the study. In this interview, the first three inclusion criteria and the last exclusion criterion are veri- fied. After receiving patients' signed informed consent, patients are invited for a second interview, in which the last inclusion criterion and the second exclusion criterion are investigated by the Structured Clinical Interview for DSM-IV Axis I Disorders/Patient edition (SCID-I/P) administered by independent psychologists. These psy- chologists make the final decision based on the results of the SCID-I/P whether patients' UPS can be classified as an undifferentiated somatoform disorder or as a chronic pain disorder and whether this disorder is the principal DSM- IV-TR classification. If undifferentiated somatoform disor- der or chronic pain disorder is the principal DSM-IV-TR classification, then patients complete the self-report ques- tionnaire for DSM-IV Axis II personality disorders (VKP). Right before the start of each next training, the newly included patients fill in the questionnaires. Subsequently, an independent statistician randomizes them to either the group training or waiting list with a computer-based 1:1 ratio randomization procedure. The results of this rand- omization procedure are sent to the patient by letter. If randomization leads to starting with the group training, then an invitation for the group training is enclosed in the randomization letter. After the group training or after a waiting-period of the same length as the group training, all patients fill in the questionnaires for the second time. After filling in the outcome measurements for the second time, the patients on the waiting list are invited to the group training. They follow the group training after their waiting period together with the newly included patients randomized to the group training in the most recent ran- domization. For patients on the waiting list, a longer wait- ing period is not feasible, because the study is conducted in the daily practice of a real life mental healthcare insti- tution. By combining the patients assigned by the previ- ous randomization to the waiting list with the patients assigned by the next randomization to the group training in the same training, the patients in both conditions receive exactly the same training. After completing the training, all patients fill in follow-up measurements after three months and after one year. Experimental condition: group training The group training [17] is based on the consequences model, which labels psychosocial stress as consequences rather than as causes of UPS to prevent the suggestion that 'its all in the head'. The original consequences model [18] assumes that UPS induces irrational beliefs regarding the symptoms resulting in consequences, which maintain or increase UPS (see black arrows in Figure 2). Its implemen- tation in an individual therapy starts with beliefs labeling them as irrational, disputing them and replacing them with rational ones. Subsequently, other consequences are changed to break the vicious circle [19]. The ultimate goal is to reduce physical symptoms. We assume that this original consequences model has not completely succeeded in preventing the 'its all in the head' suggestion. After all, patients might perceive the focus on irrational beliefs still as 'its all in the head'. Patients might Page 4 of 9 (page number not for citation purposes)