I am doing Ph D on MBRP therapy and want to assess its effect on motivation level of opioid addicts. but i don't have a suitable questionnaire to assess motivation level of opioid addicts. please suggest me a tool to accomplish my research purpose.
I think you have to specify what you mean by "motivation level", i.e., motivation to what (e.g., to participate in the study, to reduce opiate use, to quit opiate use??). Some simple scales used in MI are "how important it is for you to make changes in....." (motivation) and "how confident you are in making the changes in..." (self-efficacy). The questions are often scored on 0 - 10 scales and often used as clinical tools. I believe that such simple tools can be used in Research designs as well (e.g. to Control for motivation and self-efficacy).