Control Group Design in a Complex Intervention Study: Challenges, Dilemmas and Possible Solutions

Abstract Background The use of a control group is one of the most critical components of an RCT. The control conditions may change over time and include assessment interviews and standard stroke treatment. Therefore, the control group should be monitored and described in as much detail as the intervention group. It is important to find ways to reduce the risk of study-induced influence on the members of the control group. The aim of this study was to explore the possible influence of the assessment interviews on the adjustment of the members of a control group in an RCT exploring psychosocial well-being following stroke. Methods Fifteen participants in the control group of the RCT, six women and nine men, aged 29-88 years, were interviewed in narrative semi-structured interviews. Ricoeur’s interpretation theory guided the analysis. Results The perceived influence of the assessment interviews on the control group varied considerably. Two different themes with subthemes were identified, describing the influence of the assessment interviews in the control group. Theme one described how participants emphasized the perceived influence of the assessment interviews that served as a safety net, enhanced their awareness and understanding, facilitated their adjustment after stroke, encouraged them to seek support, and allowed them to vent their disappointment of having been allocated to the control group. Theme two described participants’ experiences of handling their adjustment process on their own without describing any influence of the assessment interviews on their condition. These participants highlighted mild strokes, spontaneous recovery, setting own goals, support from family and friends and supporting research. Conclusions In view of the design challenges in RCTs, it seems important to explore in depth how to design assessment interviews with control group members without introducing risk of bias, and to uphold rigor and stringency in the trials.