Letter to the editor of Substance Abuse Treatment, Prevention and Policy (re: A cost-benefit/cost-effectiveness analysis of proposed supervised injection facilities in Ottawa, Canada) Trevor Arnason, University of Ottawa 10 November 2014 We read the article by Jozaghi et al. (1) with interest in regards to evidence for the differential effects of supervised injection facilities on HIV and/or HCV transmission compared to existing programs that provide needle distribution. We have concerns about the scientific rigour of this study which undermines the authors’ conclusions. Key information for interpreting the results of economic evaluations such as the perspective of the analysis, the time-horizon, discounting methods and the calculation of incremental cost-effectiveness ratios, benefit-cost and cost-benefit ratios are absent in the published study. As no value is placed on health outcomes, such as in quality-adjusted life years (QALYs), it is difficult to determine the potential impact of supervised injection facilities in Ottawa and assess cost-effectiveness against commonly used thresholds. Furthermore, there is inadequate verification and minimal rationale provided for parameter values used in the cost-benefit/effectiveness models. Notably, it appears that an inaccurate 14% baseline estimate of the needle sharing rate (s or λ) was taken, in error, from a 2012 study (2). That study estimated the rate of needle sharing in Ottawa to be 4.5% (range 3.5% to 5.6%). The authors incorrectly assert that their estimate is conservative or an underestimate. We question estimates of other parameter values for which a clear justification for their use is not provided. This includes the percentage of HCV and HIV infection from a single injection, percentage of needles not cleaned, number of needles in circulation and lifetime cost-savings per HIV and HCV case. For example, the estimate of the percentage of needles not cleaned (d) is taken from two separate studies of needle-exchange programs operating in different contexts in the 1990s. These two studies produced divergent estimates for the same parameter value, but there is no explanation of how this discrepancy was reconciled to arrive at the estimate used in the models. Although a sensitivity analysis applied to the needle sharing rate demonstrated the utility of this approach, none was conducted for the other parameters. This is a significant omission given the dynamic and hypothetical circumstances being modelled in this analysis. Further sensitivity analyses would provide some assurance that varying parameter estimates will not alter the conclusions about the economic attractiveness of establishing supervised injection facilities in Ottawa. Given the lack of complete information on methodology and rationale for the chosen parameter estimates, we find it impossible to draw meaningful conclusions from this study. We remain interested in high-quality research on this topic in the Ottawa setting, but studies that do not adhere to standard practices for cost-benefit/effectiveness analyses risk confusing the interpretation of results and misguiding public health policy. Trevor Arnason, Public Health and Preventive Medicine Resident, University of Ottawa Beate Sander, Scientist, Public Health Ontario Doug Sider, Medical director, Communicable Disease Prevention and Control, Public Health Ontario Vera Etches, Deputy Medical Officer of Health, Ottawa Public Health References: 1) Jozaghi et al. A cost-benefit/cost-effectiveness analysis of proposed supervised injection facilities in Ottawa, Canada. Substance Abuse Treatment, Prevention, and Policy 2014 9:31 2) Bayoumi AM, Strike C. Report of the Toronto and Ottawa supervised consumption assessment study. St. Michael’s Hospital; 2012. Available from: http://www.stmichaelshospital.com/pdf/research/SMH-TOSCA-report.pdf Competing interests No competing interests to declare.