Background Retention of participants is essential to ensure the statistical power and internal validity of clinical trials. Poor participant retention reduces power and can bias the estimates of intervention effect. There is sparse evidence from randomised comparisons of effective strategies to retain participants in randomised trials. Currently, non-randomised evaluations of trial retention interventions embedded in host clinical trials are rejected from the Cochrane review of strategies to improve retention because it only included randomised evaluations. However, the systematic assessment of non-randomised evaluations may inform trialists’ decision-making about retention methods that have been evaluated in a trial context.Therefore, we performed a systematic review to synthesise evidence from non-randomised evaluations of retention strategies in order to supplement existing randomised trial evidence. Methods We searched MEDLINE, EMBASE, and Cochrane CENTRAL from 2007 to October 2017. Two reviewers independently screened abstracts and full-text articles for non-randomised studies that compared two or more strategies to increase participant retention in randomised trials. The retention trials had to be nested in real ‘host’ trials ( including feasibility studies) but not hypothetical trials. Two investigators independently rated the risk of bias of included studies using the ROBINS-I tool and determined the certainty of evidence using GRADE (Grading of Recommendations Assessment, Development and Evaluation) framework. Results Fourteen non-randomised studies of retention were included in this review. Most retention strategies (in 10 studies) aimed to increase questionnaire response rate. Favourable strategies for increasing questionnaire response rate were telephone follow-up compared to postal questionnaire completion, online questionnaire follow-up compared to postal questionnaire, shortened version of questionnaires versus longer questionnaires, electronically transferred monetary incentives compared to cash incentives, cash compared with no incentive and reminders to non-responders (telephone or text messaging). However, each retention strategy was evaluated in a single observational study. This, together with risk of bias concerns, meant that the overall GRADE certainty was low or very low for all included studies. Conclusions This systematic review provides low or very low certainty evidence on the effectiveness of retention strategies evaluated in non-randomised studies. Some strategies need further evaluation to provide confidence around the size and direction of the underlying effect.

Background Studies show that following lower-limb joint replacement surgery most patients fail to achieve the recommended amount of physical activity. This study aims to describe and evaluate physical activity interventions in individuals that have undergone hip or knee joint replacement due to osteoarthritis. Design A systematic review. Protocol registration PROSPERO CRD42016033498 (http://www.crd.york.ac.uk/PROSPERO/). Experimental and observational study designs investigating physical activity interventions after joint replacement were considered. The primary outcome was self-reported or objectively measured change in physical activity. Two reviewers extracted the data and appraised the methodological quality of the included studies. Results 11873 studies were screened. Seven studies with 627 participants, aged 50 to 85 years met the review criteria. Five randomised control trial, one longitudinal quasi-experimental study with a control group and one pre/post-test study with control group. Interventions included health coaching, a walking programme, a behavioural change intervention and an alpine skiing intervention delivered between 6 and 24 weeks.Two studies reported change in physical activity using patient activity diaries and five used objective accelerometer data. Statistical pooling of the study results was not possible. However, all studies showed an increase in time spent being physically active in the intervention groups. One study also reported an increase in vitality.Conclusions Few studies have investigated physical activity interventions after hip or knee joint replacement, and evidence for the effectiveness of physical activity interventions post-replacement is low. High quality studies are needed in this area to explore the potential benefits presented within this review.

Background Studies show that following lower-limb joint replacement surgery most patients fail to achieve the recommended amount of physical activity. This study aims to describe and evaluate physical activity interventions in individuals that have undergone hip or knee joint replacement due to osteoarthritis. Design A systematic review. Protocol registration PROSPERO CRD42016033498 (http://www.crd.york.ac.uk/PROSPERO/). Experimental and observational study designs investigating physical activity interventions after joint replacement were considered. The primary outcome was self-reported or objectively measured change in physical activity. Two reviewers extracted the data and appraised the methodological quality of the included studies. Results 11873 studies were screened. Seven studies with 627 participants, aged 50 to 85 years met the review criteria. Five randomised control trial, one longitudinal quasi-experimental study with a control group and one pre/post-test study with control group. Interventions included health coaching, a walking programme, a behavioural change intervention and an alpine skiing intervention delivered between 6 and 24 weeks.Two studies reported change in physical activity using patient activity diaries and five used objective accelerometer data. Statistical pooling of the study results was not possible. However, all studies showed an increase in time spent being physically active in the intervention groups. One study also reported an increase in vitality.Conclusions Few studies have investigated physical activity interventions after hip or knee joint replacement, and evidence for the effectiveness of physical activity interventions post-replacement is low. High quality studies are needed in this area to explore the potential benefits presented within this review.