Andersson et al. BMC Public Health 2011, 11:215 http://www.biomedcentral.com/1471-2458/11/215 did introduce some costs of its own, these costs were off- set by greater productivity levels both at paid work and in the domestic realm. Thirty-six percent of the partici- pants in the treatment condition were clinically improved and for each case of clinical improvement in IBS symp- toms $16,806 of societal costs were saved. Irrespective of modeled scenario and choice of imputation method the online CBT intervention was associated with cost offsets, demonstrating robustness of our findings. The control group showed similar improvements and cost-savings after being crossed over to treatment. The results from this trial differ from the McCrone et al. [7] and Creed et al. [6] studies. In the Creed et al. study, significant reductions in health care costs were found at the one-year follow-up but no significant reductions in work loss for the psychotherapy group. One possible explanation for this difference could be that this study used a broader perspective including both work cutback as well as domestic loss in the cost- effectiveness analysis. In the McCrone et al. study, the CBT group did not show any significant reductions in work loss and the treatment was not cost-effective beyond 3-month follow-up. In the original treatment study that the McCrone et al. report was based on, the participants’ improvements in symptom actually declined after the 3-month follow-up [27]. In contrast, the participants in our study demonstrated long-term maintenance of symptom reduction that could explain the long-term cost effectiveness. By and large, the results from this study provide additional evidence for internet-delivered CBT as a cost-effective treatment alternative for IBS. Our study has several limitations. First, the cost data was collected using self-reports and the accuracy of this methodology can be open-to-question. However, the recall period was relatively short (4 weeks) and there is no reason to assume that inaccuracies overly bias any of the two treatment conditions. In addition, previous research studies have indicated that self-reports are as reliable as administratively recorded data [28]. The TIC- P has been used in numerous studies [29-31] and has the advantage of being a broad measure covering health care uptake and productivity losses both in paid work as well as in the domestic realm. Therefore, the self-report methodology could be regarded as a feasible choice of measurement. Secondly, the use of 50% decline in IBS symptoms measured as criterion for clinically significant improvement might be inappropriate. This criterion has been used in several trials [20] of psychological treat- ment but other measures of clinically significant improvement have been proposed. The participants’ subjective experience of “adequate relief” [32] has been used in both pharmacological [33] and psychological trials [9]. A 50 point reduction in score on the IBS-SSS Page 6 of 7 [34] has also been used as clinically significant improve- ment in symptoms. These differences in determining a clinically significant outcome are problematic as they make it difficult to compare trials and treatments. It would therefore have been preferable if at least one of the adequate relief and IBS-SSS measures had been included in this study. Thirdly, the control condition participants were randomized to a waiting list and were therefore aware that they would eventually receive the treatment. This factor could possibly have an impact on the cost-effectiveness results since the study design did not allow control for attention and expectancy of improvement. A proper attention control condition would have provided a more reliable estimate the cost- effectiveness of the specific treatment used. Fourthly, the calculations are based on internet CBT in a research setting and the real market price of such interventions is still unknown. Fifth, we did not directly ask the parti- cipants about their gross earning but instead used the average Swedish salary based on the participant’s educa- tion level. This lack of information could possible pro- duce errors in the mean cost calculations regarding production losses. However, the participants were ran- domized and potential errors should not affect the between group ICER estimations. Finally, as the control group was crossed over to treatment no comparison group was available at the 3-month and 1 year follow- up. The short experimental time period makes the extrapolated estimates of long-term cost-effectiveness somewhat less reliable. However, when repeating the analyses with 3-month and 1 year follow-up clinical data, the scatter of the simulated ICERs over the cost- effectiveness plane did not differ in any substantial way and would not change our conclusions. Conclusions To summarize, the findings from this study indicate that internet-delivered CBT for IBS can both be effective in treating IBS and generate cost savings for the society. Future evaluations should continue to investigate the cost-effectiveness as well as look more closely at the economic ramifications with regard to favorable treat- ment response. More research is also needed to expand our knowledge concerning the economic impact of internet-delivered CBT for IBS. We recommend that future studies use a more potent placebo condition and longer follow-up periods. Acknowledgements None. Author details 1Department of Clinical Neuroscience, Stockholm Center for Psychiatry Research, Karolinska Institutet, Stockholm, Sweden. 2Department of Epidemiology and Biostatistics, EMGO Institute for Health and Health Care