Recruitment of adolescents and young persons with chronic conditions (CC) to research studies is a known challenge (1). For intervention studies, recruitment rates in this population have ranged from 10–50% (2–6). Factors considered to affect adolescents’ participation in intervention studies may be clinical (i.e. disease severity) (7), demographic (i.e. household income and geographic location), and individual (i.e. personal incentives and school performance) (8–11). Moreover, an additional barrier to recruitment is that participation in intervention studies means the adolescent has to engage in their illness (12). For many adolescents this is challenging, as young persons want to live their lives as a healthy normal teens, and not spend excessive time thinking about their illness (13).
In most settings, adolescents living with a CC have to transfer their care from a pediatric to an adult setting at age 18. During this transitional phase, these individuals are subject to several risks, such as care gaps in medical follow-up (14), increased healthcare utilization (15, 16), and difficulties in achieving educational and vocational milestones (17). To prepare adolescents for the transfer to adult care and transition to adulthood, transition programs are advocated (18–20).
Randomized controlled trials (RCT) have been conducted to evaluate the effectiveness of transition programs, with positive effects in disease-related knowledge, self-efficacy, self-management (21) and reduced delay in transfer to adult care (22). However, RCTs evaluating these interventions have lacked reporting of components to assess external validity such as representativeness of their samples and response rates (21, 23), so generalizability of current transition programs is limited.
In addition to generalizability, the ‘reach’ of an intervention study is important to consider when translating findings to clinical practice. Indeed, transition programs are complex interventions because of their numerous interacting components, challenging behaviours required by those delivering and receiving the intervention, and because they target different organizational levels (i.e. pediatric and adult care) (24). When evaluating a complex intervention, effectiveness data is not enough to understand if the intervention was successful. This is because implementation of the intervention might differ between individual patients, and sites over time (25). Determining the reach of an intervention (and the full RCT) is an essential element in evaluating of complex interventions, as it provides knowledge of the absolute number, proportion and representativeness of individuals who were willing to participate in the study (26).
When evaluating the effectiveness of new interventions such as transition programs, RCTs are viewed as the gold standard (21, 27, 28). However, RCTs are vulnerable for selection bias. In trials for patients with CCs, as many as 70% of studies lacked representativeness of their study samples (29), with participants often healthier than patients seen in clinical practice (29, 30). The lack of knowledge on reach and representativeness of participants in transition programs (21, 23) poses several challenges. Firstly, if samples do not represent patients in real life settings, clinicians cannot assess which findings that can be translated into clinical practice (31). Secondly, RCTs are usually the basis for health economic evaluations and decisions on resource allocation in healthcare (32, 33). If samples of RCTs are biased, decision-makers risk making faulty assessments as to which interventions that are cost-effective and could be implemented into practice. Thirdly, we lack knowledge about which adolescents and sub-groups that are more difficult to recruit for complex interventions. The aim of this study was therefore to evaluate the reach and representativeness of an RCT evaluating the effectiveness of a complex intervention for adolescents with CC in transition to adulthood. Two specific objectives were formulated to achieve this aim: (i) to compare clinical and demographic characteristics of participants and non-participants in the RCT, and (ii) to describe adolescents’ reasons for participating or not participating in the RCT from their own perspective.