Abstract: We included four studies that compared SDM versus control and included a total of 1342 participants. Three studies recruited children with asthma and their care-givers, and one recruited adults with asthma. Three studies took place in the United States, and one in the Netherlands. Trial duration was between 6 and 24 months. One trial delivered the SDM intervention to the medical practitioner, and three trials delivered the SDM intervention directly to the participant. Two paediatric studies involved use of an online portal, followed by face-to-face consultations. One study delivered an SDM intervention or a clinical decision-making intervention through a mixture of face-to-face consultations and telephone calls. The final study randomised paediatric general practice physicians to receive a seminar programme promoting application of SDM principles. All trials were open-label, although one study, which delivered the intervention to physicians, stated that participants were unaware of their physicians' involvement in the trial. We had concerns about selection and attrition bias and selective reporting, and we noted that one study substantially under-recruited participants. The four included studies used different approaches to measure fidelity/intervention adherence and to report study findings. One study involving adults with poorly controlled asthma reported improved quality of life (QOL) for the SDM group compared with the control group, using the Asthma Quality of Life Questionnaire (AQLQ) for assessment (mean difference (MD) 1.90, 95% confidence interval (CI) 1.24 to 2.91), but two other trials did not identify a benefit. Patient/parent satisfaction with the performance of paediatricians was greater in the SDM group in one trial involving children. Medication adherence was better in the SDM group in two studies - one involving adults and one involving children (all medication adherence: MD 0.21, 95% CI 0.11 to 0.31; mean number of controlled medication prescriptions over 26 weeks: 1.1 in the SDM group (n = 26) and 0.7 in the control group (n = 27)). In one study, asthma-related visit rates were lower in the SDM group than in the usual care group (1.0/y vs 1.4/y; P = 0.016), but two other studies did not report a difference in exacerbations nor in prescriptions for short courses of oral steroids. Finally, one study described better odds of reporting no asthma problems in the SDM group than in the usual care group (odds ratio (OR) 1.90, 95% CI 1.26 to 2.87), although two other studies reporting asthma control did not identify a benefit with SDM. We found no information about acceptability of the intervention to the healthcare professional and no information on adverse events. Overall, our confidence in study results ranged from very low to moderate, and we downgraded outcomes owing to risk of bias, imprecision, and indirectness. Substantial differences between the four included randomised controlled trials (RCTs) indicate that we cannot provide meaningful overall conclusions. Individual studies demonstrated some benefits of SDM over control, in terms of quality of life; patient and parent satisfaction; adherence to prescribed medication; reduction in asthma-related healthcare visits; and improved asthma control. Our confidence in the findings of these individual studies ranges from moderate to very low, and it is important to note that studies did not measure or report adverse events. Future trials should be adequately powered and of sufficient duration to detect differences in patient-important outcomes such as exacerbations and hospitalisations. Use of core asthma outcomes and validated scales when possible would facilitate future meta-analysis. Studies conducted in lower-income settings and including an economic evaluation would be of interest. Investigators should systematically record adverse events, even if none are anticipated. Studies identified to date have not included adolescents; future trials should consider their inclusion. Measuring and reporting of intervention fidelity is also recommended.

Plain-language summary: We reviewed the evidence up to November 2016. We found four studies, including 1342 people, that attempted to answer this question. All participants had asthma; participants in three studies were children and those in one study were adults. Three studies took place in the United States and one in the Netherlands; studies lasted from six months to two years. Different studies used different methods of shared decision-making, including face-to-face discussions, telephone calls, and online messages. Because these studies were conducted in different ways, we were unable to combine their findings. We found evidence from individual studies indicating that shared decision-making may improve quality of life and asthma control and may reduce healthcare visits for asthma. Shared decision-making may also help people to take their asthma inhaler(s) more regularly owing to better understanding of why they need to do that. Going through this process may make people feel more satisfied with their care, as they may feel empowered about making choices. However, all of these findings were reported by different studies, and some studies showed benefit of shared decision-making, while others did not. It is important to mention that none of these studies looked into whether shared decision-making causes unwanted side effects. All four studies measured how well the shared decision-making intervention had been delivered or received but did this in different ways. We were not very confident in the quality of the evidence presented in this review. We were concerned about the small number of studies and about differences in the way included studies were designed. Also, participants knew which group they were in (i.e. shared decision-making or standard care), and this may have affected how they answered questions about their asthma during the trial. Some evidence suggests that shared decision-making might help people with asthma, but we are not sure whether it is helpful. In the future, larger studies that include adolescents while looking out for side effects, harms, and benefits should prove useful in answering this question.