Background
The rationale for the review
Objectives
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To provide a comprehensive review of retention strategies evaluated through non-randomised study designs.
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To measure the effect of strategies to promote retention in randomised trials and to explore whether the effect varied by trial setting, trial strategy and/or retention behaviour.
Methods
Criteria for considering studies for this review
Types of studies
Outcome measures
Primary outcome
Secondary outcomes
Search methods
Identification of eligible studies
Data extraction and management
Quality assessment of included studies
Data synthesis
Assessment of the overall certainty in the body of evidence
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Study limitations: downgrade all high Risk of Bias (RoB) studies by two levels; downgrade all uncertain RoB studies by one level.
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Inconsistency: assume no serious inconsistency.
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Indirectness: downgrade by one level if a proxy for actual retention is all that is presented.
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Imprecision: downgrade all single studies by one level because of the sparseness of data; downgrade further by one level if the confidence interval is wide and crosses the line where risk difference = 0.
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Reporting bias: assume no serious reporting bias.
Results
Participants and settings
Trial | Study design | Host trial (number randomised) | Disease/condition | Participants | Setting | Retention strategies (number of participants) | Outcome (retention study) | Time point(s) used in the analysis |
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1. Studies that involved a change in mode of data collection | ||||||||
Atherton 2010 [25] | Cohort study | Prevention of Pelvic Infection (POPI) trial (1329) | Chlamydia screening | Young female students | 12 universities and colleges across London | A postal follow-up questionnaire (299) Online questionnaire (1030) | Questionnaire response rate | 12 months after randomisation 4 weeks and 12 months after follow-up commenced |
Childs 2015 [26] | Cohort study | Prevention of Lower Back Pain in the Military (POLM) trial (4325) | Low back pain | Geographically dispersed soldiers in the US Army | A military training setting | Web-based survey (632) Telephone call center (571) Both the web-based and telephone survey (233) M2 database (2788) | Follow-up rate | Monthly follow-up surveys (12 weeks after training). Telephone contact with soldiers who had not responded to 3 monthly web-based surveys at the end of the first year |
Dormandy 2008 [27] | Before and after study | SHIFT (Screening for Haemoglobinopathies in the First trimester) (775) | Antenatal Sickle Cell and Thalassaemia (SCT) screening | People from minority ethnic groups and with high levels of material and social deprivation | UK primary care | Postal questionnaire completion only (61) Choice of telephone or postal completion (714) | Questionnaire response rate | 11 months after randomisation |
Johnson 2015 [28] | Before and after study | The hospital outpatient alcohol project (HOAP) (837) | Alcohol consumption | Hospital outpatients with hazardous or harmful drinking | Outpatient department of a large tertiary referral hospital in Newcastle (population 540,000), Australia | Postal questionnaire + link a web-based questionnaire (520/837) Telephone follow-up (317) | Questionnaire response rate | 6 months after randomisation 4 weeks later if questionnaire remained unreturned |
Lall 2012 [29] | Cohort study | Back Skills Training Trial (BeST) (701) | Back pain | Patients with subacute and chronic low back pain | UK primary care | Postal questionnaires Telephone interviews | Questionnaire response rate | 12 months after randomisation 6 weeks later if questionnaire remained unreturned |
Peterson 2012 [30] | Post hoc analysis method | Randomised clinical trial of elective coronary artery bypass grafting (248) | Coronary artery disease | Coronary artery bypass graft surgery patients | The New York Hospital–Cornell Medical Center | Routine follow-up approach (return to hospital for follow-up) (187) Home follow-up (61) | Follow-up rate and its impact on main trial outcome | 6-month follow-up |
2. Studies that used a different questionnaire format for follow-up | ||||||||
Bailey 2013 [31] | Before and after study | The Sexunzipped trial (2006) | Sexual well-being | Young people aged 16 to 20 years and resident in the UK | Online study | Online questionnaire (1208) A shortened version of the online questionnaire by post (798) | Retention of valid participants at 3-month follow-up | 3 months after randomisation |
3. Studies that used a different design strategy for follow-up | ||||||||
Ulmer 2008 [32] | Historically controlled study | Randomised controlled trial of a telephone-delivered behavioral intervention (153) | Hypertension | Participants with uncontrolled hypertension | New York Harbor Healthcare System | A 4-week simple run-in period before participation in the study | Drop-out rate | 12 months after randomisation |
4. Studies that used a change in mode of reminder delivery | ||||||||
Hansen 2014 [33] | Cohort study | ‘Preventive consultations for 20- to 40-year-old young adults’ randomised trial (495) | Change in health behavior | Young adults with multiple psychosocial and lifestyle problems | General practices in Denmark | Follow-up questionnaire and up to two reminders by mail (495) Telephone reminder to primary non-responders (179) | Questionnaire response rate | 1-year follow-up after randomisation |
Varner 2017 [34] | Nested cohort analysis | An RCT assessing minor traumatic brain injury (MTBI) discharge instructions (118) | Traumatic brain injury | Patients ages 18 to 64 years presenting to the ED with a chief complaint of a head injury or suspected concussion | Emergency department (ED) of an academic tertiary care hospital in Toronto, Ontario | Telephone contact (78) A reminder text message (40) | The proportional difference in loss to a follow-up between the two groups | First 4 months Final 3 months |
5. Studies that used incentives | ||||||||
Brealey 2007 [35] | Historically controlled study | DAMASK Trial (a pragmatic randomised trial to evaluate whether GPs should have direct access to MRI for patients with suspected internal derangement of the knee) (547) | Knee problems | Patients aged 18 to 55 with suspected internal derangement of the knee | General practices across North Wales, North East Scotland, and Yorkshire | No incentive (105) Unconditional direct payment of £5 to patients for the completion and return of questionnaires (442) | Completion rate of postal questionnaires | 12 months after randomisation |
Rodgers 2016 [36] | Prospective cohort study | An RCT evaluated the effectiveness of a brief social work intervention (479) | Instances of violence and heavy drinking among women | Abused women who were also heavy drinkers | Two US academic urban EDs | Cash incentives for participants enrolled during the first 8 months of the study (111) A reloadable bank card for all subsequent participants (358) | Participant completion rates of follow-up study activities and overall retention | 3-, 6- and 12-month follow-up after randomisation |
6. Studies that used multi-faceted strategies | ||||||||
Ezell 2013 [37] | Post hoc analysis method | RCT comparing asthma outcomes of students exposed to tailored asthma management versus those exposed to generic asthma management (422) | The burden of asthma | Students in grades 9 through 12 | Six Detroit public high schools | Incentives ($80 for completion of all program modules) (380). 4 retention strategies to locate missing participants (re-dials of non-working telephone numbers, Facebook, assistance from school) (125) | Attrition rate | 12-month follow-up |
Sellers 2015 [38] | Before and after study with no control group | The BAN trial was designed to evaluate the efficacy of 3 mother-to-child HIV transmission prevention strategies (2369) | HIV prevention | Pregnant women who tested HIV-positive and their infants | Four antenatal clinics Lilongwe, Malawi | Routine strategies (support groups, home visits) (1686) Intensive tracing efforts (638) | Attrition rate | 28 weeks after randomisation |
Design of the included retention studies
Risk of bias assessment
Handling missing data
Assessment of reporting bias
Intervention effects
Strategies that involved a change in mode of data collection
Study ID | Study design | Comparator | Intervention | Difference in response rate (primary end point) | Difference in response rate (secondary end point) |
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Johnson 2015 [28] | Before and after study | Unique hyperlink to the follow-up questionnaire plus reminders sent at 2-week intervals (6 months after randomisation) | Telephone follow-up to non-resonders (4 weeks later) | Retention before telephone follow-up was 62.1% (520/837) and 82.8% (693/837) afterward: an increase of 20.7% (173/837) | No secondary end point reported |
Childs 2015 [26] | Before and after study | 3-monthly web-based surveys sent 2 years following completion of the assigned intervention | A telephone follow-up to non-responders at the end of the first year | Adding the telephone call center resulted in an 18.6% increase in follow-up rate | No secondary end point reported |
Dormandy 2008 [27] | Before and after study | Postal questionnaire completion only | A choice of telephone or postal questionnaire completion | The response rate (11 months after randomisation) from women offered postal completion was 26% compared with 67% for women offered a choice of telephone or postal completion (41% difference). Response rate for women choosing telephone completion was 98% compared with 23% for women choosing postal completion (75% difference, 95% CI diff 70 to 80) | No secondary end point reported |
Lall 2012 [29] | Prospective cohort study | Postal questionnaire completion 12 months after randomisation. | Telephone follow-up to nonrespondents (6 weeks later) | The overall response rate increased by 14% (from 71 to 85%) after telephone follow-up | No secondary end point reported |
Atherton 2010 [25] | Prospective cohort study | Postal questionnaire completion after 12 months | Online questionnaire | The response rates to the 12-month questionnaire in the online and postal groups were 51% and 29%, respectively, 4 weeks after follow-up commenced (RR 1.78 (1.47 to 2.14)) | The response rates to the 12-month questionnaire in the online and postal groups were 72% and 59%, respectively, after 3 months |
Peterson 2012 [30] | Post hoc analysis method | Routine follow-up | Home follow-up | Home follow-up (6 months after randomisation) was effective in achieving follow-up on an additional 61 participants (25%), decreasing attrition rate to only 4% | No secondary end point reported |
Strategies that used a different questionnaire format for follow-up
Different design strategies for follow-up
Strategies that involved a change in the mode of reminder delivery
Study ID | Study design | Comparator | Intervention | Difference in response rate (primary end point) | Difference in response rate (secondary end point) |
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Hansen 2014 [33] | Prospective cohort study | A follow-up questionnaire and up to two reminders by mail | Non-responders were contacted by telephone to return postal questionnaires | Telephone contact (1 year follow-up after randomisation) raised the response by 10% from 316 (64%) to 364 (74%) | No secondary end point reported |
Varner 2017 [39] | Prospective cohort study | Participants were contacted by a conventional telephone call during the 4 months of study follow-up | Non-responders (final 3 months) were sent text message reminders of upcoming telephone follow-up for the return of postal questionnaires. | Sending text messages increased response by 22% (95% CI 5.9 to 34.7%) at 2-week follow-up | Sending text messages increased response by 17.7% (95% CI − 0.8 to 33.3%) at 4-week follow-up |
Strategies that involved incentives
Study ID | Study design | Comparator | Intervention | Difference in response rate (primary end point) | Difference in response rate (secondary end point) |
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Brealey 2007 [35] | Historical control study design | No incentive (the first 105 patients did not receive the £5 incentive) | The subsequent 442 patients received unconditional direct payment of £5 for the completion and return of questionnaires | The response rate (12 months after randomisation) following reminders for the historical controls was 78.1% (82 of 105) compared with 88.0% (389 of 442) for those patients who received the £5 payment (diff = 9.9%, 95% CI 2.3 to 19.1%). | No secondary end point reported |
Rodgers 2016 [36] | Prospective cohort study | In-person cash incentive for the first 111 participants | The subsequent 358 participants were given reloadable bank card for incentive payments | Retention rates among the card-paid participants at 6 months was 80% vs. 68% cash-paid | Retention rates among the card-paid participants at 12 months was 72% vs. 66% cash-paid |
Multi-faceted strategies
Study ID | Study design | Comparator | Intervention | Difference in response rate (primary end point) | Difference in response rate (secondary end point) |
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Ezell 2013 [37] | Post-hoc analysis method | All partcipants were offered the possibility of receiving incentives ($80) for completion of all program modules and surveys) | 4 retention strategies (re-dials of non-working telephone numbers, mailings to the student’s home, obtaining assistance from school administration and communication through Facebook) were used to reconnect with partcipants who were overdue for the 12-month follow-up surveys | The increase in overall questionnaire response (i.e. retention) rate was 21.6% at 12-month follow-up | No secondary end point reported |
Sellers 2015 [38] | Before and after study | The first 1686 participants received routine strategies (support groups, home visits, transportation to and from study visits, frequent attempts to contact clients to reschedule missed visits) | The subsequent 683 participants received enhanced intensive tracing efforts (broadcast a radio announcement in Chichewa, the local language, hiring a community educator to trace missing participants via motorcycle) | Intensive tracing efforts increased the overall response rate from 80% to 87.8% at 28 weeks after randomisation | No secondary end point reported |
Cost of retention strategies
Discussion
Summary of main results
Overall completeness and applicability of evidence
Limitations
Implication for methodological research
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The effect of telephone interviews versus online questionnaire completion on questionnaire response rate.
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The effect of home follow-up versus routine follow-up on retention rate.