Andersson et al. BMC Public Health 2011, 11:215 http://www.biomedcentral.com/1471-2458/11/215 there is little evidence regarding the economic aspects of internet-delivered CBT. Methods Sample Participants were eligible for the study if they had been diagnosed with IBS by a physician before applying for the study and if they presently fulfilled the Rome III cri- teria for IBS [13]. The Montgomery Åsberg Depression Rating Scale - Self report [MADRS-S; [14]] was used to exclude participants, fulfilling criteria for suicide idea- tion (item 9 ≥ 4), and severe depressive symptoms(total score ≥ 30). Participants fulfilling criteria for substance dependence according to Alcohol Use Disorders Identi- fication Test [AUDIT; [15]] or Drug Use Disorders Identification Test [DUDIT; [16]] and participants suf- fering from psychosis, manic episode, or anorexia were also excluded. Procedure Figure 1 displays participant flow through the selection procedure, randomization and assessments. The partici- pants were recruited through self-referral from the gen- eral adult population in Sweden. A total of 193 individuals applied for the study, 98 were interviewed and 86 were included for randomization. Telephone interviews were conducted by graduate psychology stu- dents or psychologists and included structured questions about Rome III-criteria and also the Mini-International Neuropsychiatric Interview [MINI; [17]] to assess any psychiatric co-morbidity that could be cause for exclu- sion. All interviews were reviewed by the study’s gastro- enterologist who made the final decision if a participant should be included in the study. After having been ran- domized to the treatment condition one participant underwent a colostomy and was subsequently excluded from the study and all further data analysis. Demo- graphics for the study participants are displayed in Table 1. The study included pre- and post-treatment assess- ments for the treatment condition. Follow-up data were collected at 3-month follow-up for the treatment condi- tion. After ten weeks, the participants in the control condition were crossed over to the active treatment. Fol- low-up data were also collected for all participants in the study approximately one year (15 to 18 months) after receiving the treatment. The study protocol was approved by the regional ethics committee in Stockholm, Sweden. Interventions The experimental group was given a ten-week internet- delivered cognitive behavioral treatment with therapist support via e-mail. The mean therapist time spent on Page 2 of 7 each participant was 165 minutes (SD = 85 min). The treatment consisted of graded exposure to IBS-symptoms and mindfulness exercises. The treatment protocol is further described in Ljótsson et al. [18] and Ljótsson et al. [8]. Participants in the control group took part in a discussion forum and could contact a therapist for gen- eral support if they wished (mean therapist time was 10 minutes, SD = 23). Clinical outcome The primary outcome was the Gastrointestinal Symptom rating scale-IBS version (GSRS-IBS) [19]. A clinically significant improvement was defined as a 50% reduction of GSRS-IBS score [20]. Cost assessment Cost data were obtained with the Trimbos and Institute of Medical Technology Assessment Cost Questionnaire for Psychiatry (TIC-P) [21]. In this questionnaire, partici- pants report their health care consumption during the last month (e.g. GP visits), as well as time spent in infor- mal health enhancing activities (e.g. self-help groups and informal care from friends). Participants also report their level of sick leave and reduced work capacity both at work and in the domestic realm and unemployment status during the last month. These self-reports were used to estimate the costs of each participant’s health care consumption, work loss, and work cutback. Medication costs were based on the free market price in Sweden. Costs from health service visits were estimated using established tariffs in Sweden. The human capital approach was used for valuation of the productivity losses, which means that monetary losses associated with work loss and work cutback were based on the participants’ gross earning for the full length of their sick leave [22]. Gross earnings were estimated using the average salary in Sweden by education level. Domes- tic losses were estimated at $ 13.17 per hour, reflecting the free market price of domestic help [23]. The costs were originally computed in Swedish Crowns and then converted into US $ using the purchasing power parities of the OECD for the reference year 2008 [24]. The direct medical costs associated with the interven- tion were mainly driven by the costs of therapists. In this study, the therapists were graduate psychology students under supervision, but in the analysis we used the full economic cost price of a licensed clinical psychologist. The time the therapist spent on treating the partici- pants was registered and multiplied by this cost. We also estimated the costs of the participants’ time, again at $13.17/hour, thus equating it with domestic help and assuming that people engaged in the intervention after office hours. The cost estimations of the control group