The primary outcome was the SF-36 physical function subscale (SF-36-PFS)26 analysed as a continuous variable collected at 6 months after randomisation. We chose the SF-36 based on qualitative work conducted in the feasibility phase of the study.24 We have reported that parents and participants ‘commented that the school attendance primary outcome did not accurately reflect what they were able to do, particularly if they were recruited during, or had transitioned to, A levels during the study.’ In addition, ‘we were aware of some participants who had chosen not to increase school attendance despite increased activity.’ We therefore concluded that: ‘trials involving 17 and 18 year olds should consider alternative primary outcome measures to school attendance as it is difficult to assess for those transitioning from General Certificate of Secondary Education to A levels, and may not be appropriate for those who do not consider school attendance their primary goal.’ At this stage, our recommendation was that a ‘full study uses other primary outcomes, such as the SF-36 or the Chalder Fatigue Scale and uses school attendance as a secondary outcome.’ These findings informed our application for our ethical amendment to a full study in 2011 (see online supplementary table 1) and were published in our feasibility paper in 2013.24
Qualitative interviews with Specialist Medical Intervention and Lightning Evaluation (SMILE) participants then formed part of a larger study which described the conceptual model for paediatric CFS/ME.27 In this study, physical activity (or disability) is described by children as being pivotal because of the impacts on social participation and emotional well-being. While school was deemed to be an important contextual factor, these qualitative results led us to choose the SF-36-PFS as a primary outcome with school attendance as a secondary outcome. There was no analysis of any outcome data during or after the feasibility phase until the entire trial was completed.
Secondary outcomes were the SF-36-PFS at 3 and 12 months, and school attendance (days per week), the Chalder Fatigue Scale,28 pain (visual analogue scale), Hospital Anxiety and Depression Scale (HADS),29 Spence Children’s Anxiety Scale (SCAS)30 and quality-adjusted life-years (QALY, derived from the EQ-5D-Y)31 at 3, 6 and 12 months. At 3, 6 and 12 months parents completed an adapted four-item Work Productivity and Activity Impairment: General Health questionnaire (V2.0)32 and a resource use questionnaire assessing their child’s health service use (eg, general practitioner or specialist care), educational service use (eg, school counsellor), health-related travel and other family costs.
