Academy of Medical Sciences of I.R. Iran Archives of Iranian Medicine 1029-2977 21 8 2018 08 01 Comparative Effectiveness Study in Multiple Sclerosis Patients Using Instrumental Variable Analysis 368 375 EN Hamed Hosseini Mohammad Ali Mansournia Seyed Massood Nabavi Ali Asghar Akhlaghi Jaleh Gholami Kazem Mohammad Reza Majdzadeh Journal Article 2018 04 28 2018 05 19 Randomized clinical trials are considered the ideal source for generation of robust evidence for clinical and public health decision making. Estimation of treatment effect in observational studies is always subject to varying degrees of bias due to lack of random allocation, blindness, precise definition of intervention, as well as the existence of potential unknown and unmeasured confounding variables. Unlike other conventional methods, instrumental variable analysis (IVA), as a method for controlling confounding bias in non-randomized studies, attempts to estimate the treatment effect with the least bias even without knowing and measuring the potential confounders in the causal pathway. In this paper, after understanding the main concepts of this approach, it has been attempted to provide a method for analyzing and reporting the IVA for clinical researchers through a simplified example. The data used in this paper is derived from the clinical data of the follow-up of multiple sclerosis (MS) patients treated with two class of interferon.