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Meta-Analysis
. 2021 Mar 6;3(3):MR000032.
doi: 10.1002/14651858.MR000032.pub3.

Strategies to improve retention in randomised trials

Katie Gillies  1 , Anna Kearney  2 , Ciara Keenan  3 , Shaun Treweek  1 , Jemma Hudson  1 , Valerie C Brueton  4 , Thomas Conway  5 , Andrew Hunter  6 , Louise Murphy  6 , Peter J Carr  6 , Greta Rait  7 , Paul Manson  8 , Magaly Aceves-Martins  1
Affiliations
Meta-Analysis

Strategies to improve retention in randomised trials

Katie Gillies et al. Cochrane Database Syst Rev. .

Abstract

Background: Poor retention of participants in randomised trials can lead to missing outcome data which can introduce bias and reduce study power, affecting the generalisability, validity and reliability of results. Many strategies are used to improve retention but few have been formally evaluated.

Objectives: To quantify the effect of strategies to improve retention of participants in randomised trials and to investigate if the effect varied by trial setting.

Search methods: We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Scopus, PsycINFO, CINAHL, Web of Science Core Collection (SCI-expanded, SSCI, CPSI-S, CPCI-SSH and ESCI) either directly with a specified search strategy or indirectly through the ORRCA database. We also searched the SWAT repository to identify ongoing or recently completed retention trials. We did our most recent searches in January 2020.

Selection criteria: We included eligible randomised or quasi-randomised trials of evaluations of strategies to increase retention that were embedded in 'host' randomised trials from all disease areas and healthcare settings. We excluded studies aiming to increase treatment compliance.

Data collection and analysis: We extracted data on: the retention strategy being evaluated; location of study; host trial setting; method of randomisation; numbers and proportions in each intervention and comparator group. We used a risk difference (RD) and 95% confidence interval (CI) to estimate the effectiveness of the strategies to improve retention. We assessed heterogeneity between trials. We applied GRADE to determine the certainty of the evidence within each comparison.

Main results: We identified 70 eligible papers that reported data from 81 retention trials. We included 69 studies with more than 100,000 participants in the final meta-analyses, of which 67 studies evaluated interventions aimed at trial participants and two evaluated interventions aimed at trial staff involved in retention. All studies were in health care and most aimed to improve postal questionnaire response. Interventions were categorised into broad comparison groups: Data collection; Participants; Sites and site staff; Central study management; and Study design. These intervention groups consisted of 52 comparisons, none of which were supported by high-certainty evidence as determined by GRADE assessment. There were four comparisons presenting moderate-certainty evidence, three supporting retention (self-sampling kits, monetary reward together with reminder or prenotification and giving a pen at recruitment) and one reducing retention (inclusion of a diary with usual follow-up compared to usual follow-up alone). Of the remaining studies, 20 presented GRADE low-certainty evidence and 28 presented very low-certainty evidence. Our findings do provide a priority list for future replication studies, especially with regard to comparisons that currently rely on a single study.

Authors' conclusions: Most of the interventions we identified aimed to improve retention in the form of postal questionnaire response. There were few evaluations of ways to improve participants returning to trial sites for trial follow-up. None of the comparisons are supported by high-certainty evidence. Comparisons in the review where the evidence certainty could be improved with the addition of well-done studies should be the focus for future evaluations.

PubMed Disclaimer

Conflict of interest statement

Two of the review authors (ST and GR) are authors on two of the eligible studies (Bailey 2013; Treweek 2020a). There are no other conflicts to declare.

Figures

1
1
1 Included studies flow diagram.
2
2
'Risk of bias' summary: review authors' judgements about each risk of bias item for each included study.
3
3
'Risk of bias' graph: review authors' judgements about each risk of bias item presented as percentages across all included studies.
1.1
1.1. Analysis
Comparison 1: A ‐ Questionnaire Design: Short vs usual questionnaire, Outcome 1: Retention
2.1
2.1. Analysis
Comparison 2: A ‐ Questionnaire Design: Addition of diary to usual follow up vs usual follow‐up, Outcome 1: Retention
3.1
3.1. Analysis
Comparison 3: A ‐ Questionnaire Design: Question order, condition first vs generic first questions, Outcome 1: Retention
4.1
4.1. Analysis
Comparison 4: A ‐ Data Collection Frequency and Timing: Timing of questionnaire delivery, Outcome 1: Retention
5.1
5.1. Analysis
Comparison 5: A ‐ Data Collection Location and Method: Postal follow‐up vs clinic follow‐up, Outcome 1: Retention
6.1
6.1. Analysis
Comparison 6: A ‐ Data Collection Location and Method: Telephone follow‐up vs postal questionnaire, Outcome 1: Retention
6.2
6.2. Analysis
Comparison 6: A ‐ Data Collection Location and Method: Telephone follow‐up vs postal questionnaire, Outcome 2: Retention ‐ sensitivity analysis removing quasi‐RCTs
7.1
7.1. Analysis
Comparison 7: A ‐ Data Collection Location and Method: First class vs second class outward mailing, Outcome 1: Retention
8.1
8.1. Analysis
Comparison 8: A ‐ Data Collection Location and Method: Return postage, Outcome 1: Retention
9.1
9.1. Analysis
Comparison 9: A ‐ Data Collection Location and Method: Use of self‐sampling kits, Outcome 1: Retention
10.1
10.1. Analysis
Comparison 10: B ‐ Reminders: Electronic reminder vs usual follow‐up, Outcome 1: Retention
11.1
11.1. Analysis
Comparison 11: B ‐ Reminders: Action oriented electronic reminder vs standard electronic reminder, Outcome 1: Retention
12.1
12.1. Analysis
Comparison 12: B ‐ Reminders: Personalised reminder vs non‐personalised reminder, Outcome 1: Retention
13.1
13.1. Analysis
Comparison 13: B ‐ Reminders: Telephone reminder vs usual follow‐up, Outcome 1: Retention
14.1
14.1. Analysis
Comparison 14: B ‐ Reminders: Telephone reminder vs postal reminder, Outcome 1: Retention
15.1
15.1. Analysis
Comparison 15: B ‐ Prompts: Electronic prompt vs no prompt, Outcome 1: Retention
16.1
16.1. Analysis
Comparison 16: B ‐ Prompts: Telephone prompt vs usual follow‐up, Outcome 1: Retention
17.1
17.1. Analysis
Comparison 17: B ‐ Prompts: Prenotification card vs no card, Outcome 1: Retention
18.1
18.1. Analysis
Comparison 18: B ‐ Prompts: Sticker vs no sticker, Outcome 1: Retention
19.1
19.1. Analysis
Comparison 19: B ‐ Prompts: Personalised prompt vs usual follow‐up, Outcome 1: Retention
20.1
20.1. Analysis
Comparison 20: B ‐ Prompts: Electronic prompts vs electronic reminders, Outcome 1: Retention
21.1
21.1. Analysis
Comparison 21: B ‐ Monetary incentives: Addition of monetary incentives vs usual follow‐up, Outcome 1: Retention
21.2
21.2. Analysis
Comparison 21: B ‐ Monetary incentives: Addition of monetary incentives vs usual follow‐up, Outcome 2: Retention‐ sensitivity anlysis removing quasi‐RCTs
22.1
22.1. Analysis
Comparison 22: B ‐ Monetary incentives: Addition of monetary incentives to all trial arms, Outcome 1: Retention
23.1
23.1. Analysis
Comparison 23: B ‐ Monetary incentives: Addition of monetary incentives vs addition of monetary reward, Outcome 1: Retention
24.1
24.1. Analysis
Comparison 24: B‐ Monetary incentives: Addition of monetary reward vs usual follow‐up, Outcome 1: Retention
24.2
24.2. Analysis
Comparison 24: B‐ Monetary incentives: Addition of monetary reward vs usual follow‐up, Outcome 2: Retention ‐ sensitivity analysis removing quasi‐RCTs
25.1
25.1. Analysis
Comparison 25: B ‐ Monetary incentives: Addition of monetary rewards to all trial arms, Outcome 1: Retention
26.1
26.1. Analysis
Comparison 26: B ‐ Monetary incentives: Addition of monetary incentives vs lottery, Outcome 1: Retention
27.1
27.1. Analysis
Comparison 27: B ‐ Monetary incentives: Lottery vs usual follow‐up, Outcome 1: Retention
28.1
28.1. Analysis
Comparison 28: B ‐ Monetary incentives: Addition of lottery to both trial arms, Outcome 1: Retention
29.1
29.1. Analysis
Comparison 29: B ‐ Non‐monetary incentives: Addition of pen vs usual follow‐up, Outcome 1: Retention
30.1
30.1. Analysis
Comparison 30: B ‐ Non‐monetary incentives: Addition of societal benefit message vs usual follow‐up, Outcome 1: Retention
31.1
31.1. Analysis
Comparison 31: B ‐ Non‐monetary incentives: Certificate of appreciation vs usual follow‐up, Outcome 1: Retention
32.1
32.1. Analysis
Comparison 32: B ‐ Maintaining participant engagement: Newsletter vs usual follow‐up, Outcome 1: Retention
33.1
33.1. Analysis
Comparison 33: B ‐ Maintaining participant engagement: Offer of receiving trial results vs usual follow‐up, Outcome 1: Retention
34.1
34.1. Analysis
Comparison 34: B‐ Maintaining Participant Engagement: Cover letter including a social incentive vs standard cover letter, Outcome 1: Retention
35.1
35.1. Analysis
Comparison 35: B ‐ Maintaining participant engagement: Varying signatory on cover letter, Outcome 1: Retention
36.1
36.1. Analysis
Comparison 36: B ‐ Maintaining participant engagement: Addition of a deadline vs usual follow‐up, Outcome 1: Retention
37.1
37.1. Analysis
Comparison 37: B ‐ Maintaining participant engagement: Addition of an estimate of time to complete vs no addition, Outcome 1: Retention
38.1
38.1. Analysis
Comparison 38: B. Maintaining participant engagement: Brown vs white envelope, Outcome 1: Retention
39.1
39.1. Analysis
Comparison 39: B ‐ Maintaining participant engagement: Post‐it note vs usual follow‐up, Outcome 1: Retention
40.1
40.1. Analysis
Comparison 40: B ‐ Maintaining participant engagement: Inclusion of trial newspaper article vs usual follow‐up, Outcome 1: Retention
41.1
41.1. Analysis
Comparison 41: B. Maintaining participant engagement: Frequency of telephone contact, Outcome 1: Retention
42.1
42.1. Analysis
Comparison 42: B ‐ Maintaining participant engagement: Request for collateral (concomitant), Outcome 1: Retention
43.1
43.1. Analysis
Comparison 43: B ‐ Behavioural interventions: Theory informed cover letter vs usual cover letter, Outcome 1: Retention
44.1
44.1. Analysis
Comparison 44: B ‐ Behavioural interventions: Motivational interviewing vs usual follow‐up, Outcome 1: Retention
45.1
45.1. Analysis
Comparison 45: C ‐ Prompts: Site prompts for upcoming assessments vs usual follow‐up, Outcome 1: Retention
46.1
46.1. Analysis
Comparison 46: C ‐ Monitoring visits: On‐site monitoring vs no visits, Outcome 1: Retention
47.1
47.1. Analysis
Comparison 47: D ‐ Patient Public Involvement: Peer‐led follow‐up strategy vs usual follow‐up, Outcome 1: Retention
48.1
48.1. Analysis
Comparison 48: E ‐ Impact of recruitment: Video‐enhanced patient information vs standard information, Outcome 1: Retention
49.1
49.1. Analysis
Comparison 49: E ‐ Impact of recruitment: Optimised information vs standard information, Outcome 1: Retention
50.1
50.1. Analysis
Comparison 50: E ‐ Impact of recruitment: Addition of optimised information to both arms, Outcome 1: Retention
51.1
51.1. Analysis
Comparison 51: E ‐ Impact of recruitment: Pen vs no pen, Outcome 1: Retention
52.1
52.1. Analysis
Comparison 52: E ‐ Blinding and treatment preference: Open vs blind trial design, Outcome 1: Retention
See this image and copyright information in PMC

Comment in

References

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    1. Mitchell N, Hewitt CE, Lenaghan E, Platt E, Shepstone L, Torgerson DJ, SCOOP study team. Prior notification of trial participants by newsletter increased response rates: a randomized controlled trial. Journal of Clinical Epidemiology 2012;65(12):1348-52. [DOI: 10.1016/j.jclinepi.2012.05.008] - DOI - PubMed
Mitchell 2020a {published and unpublished data}
    1. Mitchell AS, Cook L, Dean A, Fairhurst C, Northgraves M, Torgerson D, et al. Using pens as an incentive for questionnaire return in an orthopaedic trial: an embedded randomised controlled retention trial. F1000Research 2020;9:321. [DOI: 10.12688/f1000research.23018.1] - DOI - PMC - PubMed
Mitchell 2020b {published data only}
    1. Mitchell AS, Cook L, Dean A, Fairhurst C, Northgraves M, Togerson D, et al. An embedded randomised controlled retention trial of personalised text messages compared to non-personalised text messages in an orthopaedic setting. F1000Research 2020;9:591. - PMC - PubMed
Nakash 2007 {unpublished data only}
    1. Nakash RA. A Study of Response and Non-Response to Postal Questionnaire Follow-up in Clinical Trials: Chapter 6: A Randomised Controlled Trial of a Method of Improving Response to Postal Questionnaire Follow-up in a Clinical Trial [PhD thesis]. Warwick, UK: University of Warwick, Warwick Medical School, 2007.
OPAL 2020 {unpublished data only}
    1. Goodman K. Evaluation of theory informed cover letter compared to standard cover letter.. Personal communication.
Renfroe 2002 {published and unpublished data}
    1. Renfroe EG, Heywood G, Foreman L, Schron E, Powell J, Baessler C, et al. The end-of-study patient survey: methods influencing response rate in the AVID trial. Controlled Clinical Trials 2002;23(5):521-33. - PubMed
    1. Renfroe EG, Powell J, Olarte A, Morris M, Hallstrom A. Method of administering patient surveys affects response rate. Controlled Clinical Trials 1999;20:s62. [DOI: 10.1016/s0197-2456(02)00225-8] - DOI
Rodgers 2019 {published data only}
    1. Rodgers S, Sbizzera I, Cockayne S, Fairhurst C, Lamb SE, Vernon W, et al. A study update newsletter or Post-it® note did not increase postal questionnaire response rates in a falls prevention trial: an embedded randomised factorial trial. F1000Research 2019;7:1083. [DOI: 10.12688/f1000research.14591.2] - DOI - PMC - PubMed
Salvesen 1992 {published and unpublished data}
    1. Salvesen KA adn Vatten LJ. Effect of a newspaper article on the response to a postal questionnaire. Journal of Epidemiology and Community Health 1992;46(1):86. [DOI: 10.1136/jech.46.1.86] - DOI - PMC - PubMed
Sarathy 2020 {published data only}
    1. Sarathy PP, Kottam L, Parker A, Brealey S, Coleman E, Keding A, et al. Timing of electronic reminders did not improve trial participant questionnaire response: a randomized trial and meta-analyses. Journal of Clinical Epidemiology 2020;6:eprint. - PubMed
Severi 2011 {published data only}
    1. Severi E, Free C, Knight R, Robertson S, Edwards P, Hoile E. Two controlled trials to increase participant retention in a randomized controlled trial of mobile phone-based smoking cessation support in the United Kingdom. Clinical Trials 2011;8(5):654-60. [DOI: 10.1177/1740774511416524] - DOI - PMC - PubMed
Sharp 2006 {published data only}
    1. Sharp L, Cochran C, Cotton SC, Gray NM, Gallagher ME, TOMBOLA group. Enclosing a pen with a postal questionnaire can significantly increase the response rate. Journal of Clinical Epidemiology 2006;59(7):747-54. [DOI: 10.1016/j.jclinepi.2005.10.014] - DOI - PubMed
Starr 2015 {published data only}
    1. Starr K, McPherson G, Forrest M, Cotton SC. SMS text pre-notification and delivery of reminder e-mails to increase response rates to postal questionnaires in the SUSPEND trial: a factorial design, randomised controlled trial. Trials 2015;16:295. [DOI: 10.1186/s13063-015-0808-9] - DOI - PMC - PubMed
Subar 2001 {published data only}
    1. Subar AF, Ziegler RG, Thompson FE, Johnson CC, Weissfeld JL, Reding D, et al. Is shorter always better? Relative importance of questionnaire length and cognitive ease on response rates and data quality for two dietary questionnaires. American Journal of Epidemiology 2001;153(4):404-9. [DOI: 10.1093/aje/153.4.404] - DOI - PubMed
Tai 1997 {published data only}
    1. Tai SS, Nazareth I, Haines A, Jowett C. A randomized trial of the impact of telephone and recorded delivery reminders on the response rate to research questionnaires. Journal of Public Health Medicine 1997;19(2):219-21. [DOI: 10.1093/oxfordjournals.pubmed.a024613] - DOI - PubMed
Tilbrook 2015 {published data only}
    1. Tilbrook HE, Becque T, Buckley H, MacPherson H, Bailey M, Torgerson DJ. Randomized trial within a trial of yellow 'post-it notes' did not improve questionnaire response rates among participants in a trial of treatments for neck pain. Journal of Evaluation in Clinical Practice 2015;21(2):202-4. [DOI: 10.1111/jep.12284] - DOI - PubMed
Tranberg 2018 {published data only}
    1. Tranberg M, Bech BH, Blaakær J, Jensen JS, Svanholm H, Andersen B. Preventing cervical cancer using HPV self-sampling: direct mailing of test-kits increases screening participation more than timely opt-in procedures - a randomized controlled trial. BMC Cancer 2018;18(1):273. [DOI: 10.1186/s12885-018-4165-4] - DOI - PMC - PubMed
Treweek 2020a {unpublished data only}
    1. Treweek S, Gallant S, Anderson AS. SWAT 76 evaluation: randomised evaluation of sending pre-notification cards to trial participants before a face-to-face primary outcome measurement. https://www.qub.ac.uk/sites/TheNorthernIrelandNetworkforTrialsMethodolog.... - PMC - PubMed
Watson 2017 {published data only}
    1. Watson AJ, Cook J, Hudson J, Kilonzo M, Wood J, Bruhn H, et al. A pragmatic multicentre randomised controlled trial comparing stapled haemorrhoidopexy with traditional excisional surgery for haemorrhoidal disease: the eTHoS study. Health Technology Assessment 2017;21(70):1-224. [DOI: 10.3310/hta21700] - DOI - PMC - PubMed
Whiteside 2019 {published data only}
    1. Whiteside K, Flett L, Mitchell A, Fairhurst C, Cockayne S, Rodgers S, et al, OTIS Study Group. Using pens as an incentive for trial recruitment of older adults: An embedded randomised controlled trial. F1000Research 2019;8:315. [DOI: 10.12688/f1000research.18300.1] - DOI - PMC - PubMed
Young 2020 {published data only}
    1. Young B, Bedford L, das Nair R, Gallant S, Littleford R, Robertson JF, et al. Unconditional and conditional monetary incentives to increase response to mailed questionnaires: A randomized controlled study within a trial (SWAT). Journal of Evaluation in Clinical Practice 2020;26(3):893-902. [DOI: 10.1111/jep.13230] - DOI - PubMed

References to studies excluded from this review

Abboah‐Offei 2020 {published data only}
    1. Abboah-Offei M, Bristowe K, Vanderpuye-Donton NA, Ansa G, Oppong-Agyei YD, Abas M, et al. Phase II mixed methods' feasibility cluster randomised controlled trial of a novel community-based enhanced care intervention to improve person-centred outcomes for people living with HIV in Ghana. AIDS Care 2020;32(sup 2):107-18. [DOI: 10.1080/09540121.2020.1739217] - DOI - PubMed
Alexander 2008 {published data only}
    1. Alexander GL, Divine GW, Couper MP, McClure JB, Stopponi MA, Fortman KK, et al. Effect of incentives and mailing features on online health program enrollment. American Journal of Preventive Medicine 2008;34(5):382-8. [DOI: 10.1016/j.amepre.2008.01.028] - DOI - PMC - PubMed
Arnevik 2009 {published data only}
    1. Arnevik E, Wilberg T, Urnes Ø, Johansen M, Monsen J, Karterud S. Psychotherapy for personality disorders: short-term day hospital psychotherapy versus outpatient individual therapy - a randomized controlled study. European Psychiatry 2009;24:71-8. - PubMed
Arundel 2017 {published data only}
    1. Arundel C, Jefferson L, Bailey M, Cockayne S, Hicks K, Loughrey L, et al. A randomized, embedded trial of pre?notification of trial participation did not increase recruitment rates to a falls prevention trial. Journal of Evaluation in Clinical Practice 2017;23(1):73-8. [DOI: 10.1111/jep.12576] - DOI - PubMed
Atherton 2010 {published data only}
    1. Atherton H, Oakeshott P, Aghaizu A, Hay P, Kerry S. Use of an online questionnaire for follow-up of young female students recruited to a randomised controlled trial of chlamydia screening. Journal of Epidemiology and Community Health 2010;64(580):e584. - PubMed
Aysola 2018 {published data only}
    1. Aysola J, Tahirovic E, Troxel AB, Asch DA, Gangemi K, Hodlofski AT, et al. A randomized controlled trial of opt-In versus opt-out enrollment into a diabetes behavioral intervention. American Journal of Health Promotion 2018;32(3):745-52. [DOI: 10.1177/0890117116671673] - DOI - PubMed
Barry 1996 {published and unpublished data}
    1. Barry MJ, Walker-Corkery E, Chang Y, Tyll LT, Cherkin DC, Fowler FJ. Measurement of overall and disease-specific health status: does the order of questionnaires make a difference. Journal of Health Services Research and Policy 1996;1(1):20-7. - PubMed
Bednarek 2008 {published data only}
    1. Bednarek P, Nichols M, Carlson N, Edelman A, Creinin M, Truitt S, et al. Effect of "observed start" vs. traditional "Sunday start" on hormonal contraceptive continuation rates after medical abortion. Contraception 2008;78:26-30. - PubMed
Bisla 2019 {published data only}
    1. Bisla J, Ambler G, Frank B, Gulati S, Hocken P, James M, et al. Successful and unsuccessful recruitment and retainment strategies in a UK multicentre drug trial for a rare chronic pain condition which performed above target. British Journal of Pain 2020;14(3):171-9. [DOI: 10.1177/2049463719893399] - DOI - PMC - PubMed
Bowen 2000 {published and unpublished data}
    1. Bowen D, Thornquist M, Anderson K, Barnett M, Valanis B, Goodman G, et al. The use of incentives to increase participation in a chemoprevention trial. Controlled Clinical Trials 1995;16:41s.
    1. Bowen D, Thornquist M, Goodman G, Omenn GS, Anderson K, Barnett M, et al. Effects of incentive items on participation in a randomized chemoprevention trial. Journal of Health and Psychology 2000;5(1):109-15. - PubMed
Bromley 2019 {published data only}
    1. Bromley KJ, Ogollah R, Konstantinou K, Foster N, Lewis M. The use of regular text messaging over one year to collect primary outcome data in a randomised controlled trial. Trials 2019;20(Suppl 1):12.
Chaffin 2009 {published and unpublished data}
    1. Chaffin M, Valle LA, Funderburk B, Gurwitch R, Silovsky J, Bard D. A motivational intervention can improve retention in PCIT for low-motivation child welfare clients. Child Maltreatment 2009;14(4):356-68. - PubMed
Chee 2019 {published data only}
    1. Chee W, Ji X, Kim S, Park S, Zhang J, Chee E, et al. Recruitment and retention of Asian Americans in web-based physical activity promotion programs: a discussion paper. Computers, Informatics, Nursing 2019;37(9):455-62. [DOI: 10.1097/CIN.0000000000000541] - DOI - PMC - PubMed
Cheung 2019 {published data only}
    1. Cheung YT, Weng X, Wang MP, Ho SY, Kwong AC, Lai VM, et al. Effect of prepaid and promised financial incentive on follow-up survey response in cigarette smokers: a randomized controlled trial. BMC Medical Research Methodology 2019;19:138. [DOI: 10.1186/s12874-019-0786-9] - DOI - PMC - PubMed
Cox 2003 {published data only}
    1. Cox KL, Burke V, Gorely TJ, Beilin LJ, Puddey IB. Controlled comparison of retention and adherence in home- vs center-initiated exercise interventions in women ages 40?65 years: the S.W.E.A.T. study (Sedentary Women Exercise Adherence Trial). Preventive Medicine 2003;36:17-29. - PubMed
Cox 2006 {published data only}
    1. Cox KL, Burke V, Beilin LJ, Grove JR, Blanksby BA, Puddey IB. Blood pressure rise with swimming versus walking in older women: the Sedentary Women Exercise Adherence Trial 2 (SWEAT 2). Journal of Hypertension 2006;24(2):307-14. [DOI: 10.1097/01.hjh.0000200514.25571.20] - DOI - PubMed
Cox 2008 {published and unpublished data}
    1. Cox KL, Burke V, Beilin LJ, Derbyshire AJ, Grove JR, Blanksby BA, et al. Short and long-term adherence to swimming and walking programs in older women - the Sedentary Women Exercise Adherence Trial (SWEAT 2). Preventive Medicine 2008;46(6):511-7. - PubMed
    1. Cox KL, Burke V, Beilin LJ, Grove JR, Blanksby BA, Puddey IB. Blood pressure rise with swimming versus walking in older women: the Sedentary Women Exercise AdherenceTrial 2 (SWEAT 2). Journal of Hypertension 2006;24(2):307-14. [DOI: 10.1097/01.hjh.0000200514.25571.20] - DOI - PubMed
Day 1998 {published data only}
    1. Day R, Cella D, Ganz P, Constantino J. Electronic monitoring of participant adherence in the NSABP breast cancer prevention trial (BCPT). Controlled Clinical Trials 1998;19:69s.
Diaz 2001 {published data only}
    1. Diaz E, Levine HB, Sullivan MC, Sernyak MJ, Hawkins KA, Cramer JA, et al. Use of the Medication Event Monitoring System to estimate medication compliance in patients with schizophrenia. Journal of Psychiatry & Neuroscience 2001;26(4):325-9. [PMID: ] - PMC - PubMed
Eaker 2004 {published data only}
    1. Eaker S, Adami H, Granath F, Wilander E, Sparen P. A large population-based randomized controlled trial to increase attendance at screening for cervical cancer. Cancer Epidemiology, Biomarkers & Prevention 2004;13(3):346-54. - PubMed
Edelstein 2005 {published data only}
    1. Edelstein S, Minutillo A, Pyle L, Anderson B, Wilfley D, Van Buren D, et al. Rewarding youth behaviour: implementation of incentives in the TODAY trial. Clinical Trials 2005;2:s23.
Edwards 2013 {published data only}
    1. Edwards KE, Hagen SM, Hannam J, Kruger C, Yu R, Merry AF. A randomized comparison between records made with an anesthesia information management system and by hand, and evaluation of the Hawthorne effect. Canadian Journal of Anaesthesia 2013;60(10):990-7. [DOI: 10.1007/s12630-013-0003-y] - DOI - PubMed
Farabee 2016 {published data only}
    1. Farabee D, Hawken A, Calhoun S, Veliz R, Grossman J, Zhang Y. Tracking and locating itinerant subjects with a rechargeable incentive card: results of a randomized trial. Substance Use & Misuse 2016;51(5):658-63. [DOI: 10.3109/10826084.2015.1126748] - DOI - PMC - PubMed
Ford 2006 {published and unpublished data}
    1. Ford ME, Havstad S, Vernon SW, Davis SD, Kroll D, Lamerato L, et al. Enhancing adherence among older African American men enrolled in a longitudinal cancer screening trial. Gerontologist 2006;46(4):545-50. - PubMed
    1. Ford ME, Randolph V, Hopkins-Johnson L, Eason SL, Havstad S, Jankowski M, et al. Design of a case management approach to enhance cancer screening trial retention among older African American men. Journal of Aging and Health 2004;16(5):39s-57s. - PubMed
Galaragga 2017 {published data only}
    1. Galárraga O, Sosa-Rubí SG, Kuo C, Gozalo P, González A, Saavedra B, et al. Punto Seguro: a randomized controlled pilot using conditional economic incentives to reduce sexually transmitted infection risks in Mexico. AIDS and Behavior 2017;21(12):3440-56. [DOI: 10.1007/s10461-017-1960-x] - DOI - PMC - PubMed
Gaurino 2006 {published data only}
    1. Guarino P, Elbourne D, Carpenter J, Peduzzi P. Consumer involvement in consent document development: a multicenter cluster randomized trial to assess study participants' understanding. Clinical Trials 2006;3(1):19-30. [DOI: 10.1191/1740774506cn133oa] - DOI - PubMed
Grabowski 1995 {published data only}
    1. Grabowski JP, Rhoades HP, Elk RP, Schmitz JP, Davis CP, Creson DM, et al. Fluoxetine is ineffective for treatment of cocaine dependence or concurrent opiate and cocaine dependence: two placebo-controlled, double-blind trials. Journal of Clinical Psychopharmacology 1995;15(3):163-74. - PubMed
Haines 2019 {published data only}
    1. Haines RH, Chalmers JR, Swinden R, Bradshaw LE, Montgomery AM, Williams HC. Maximising participant retention in a randomised prevention trial. Trials 2019;20(suppl.1):P-189.
Hall 1975 {published data only}
    1. Hall S, Hall R, Borden B, Hanson R. Follow-up strategies in the behavioural treatment of overweight. Behaviour Research and Therapy 1975;13:167-72. - PubMed
Hall 1978 {published data only}
    1. Hall S, Bass A, Monroe J. Continued contact and monitoring as follow-up strategies: a long-term study of obesity treatment. Addictive Behaviours 1978;3:139-47. - PubMed
Henderson 2019 {published data only}
    1. Henderson M, Waldram M, Thomas A, AlAlmmary F, Di Brito S, Ottman S, et al. Can financial incentives improve living donor follow-up?: a pilot randomized controlled trial. Transplant International 2019;32(suppl.2):199.
Hoang 2014 {published data only}
    1. Hoang U, Sheldenkar A, Leon J, Emmett E, Mckevitt C, Wolfe C. The effect of personalized care on long term loss to follow-up in a stroke register: WSC-0469. International Journal of Stroke 2014;9(Suppl 3):262.
Hoffman 1998 {published data only}
    1. Hoffman S, Burke A, Helzlsouer K, Comstock G. Controlled trial of the effect of length, incentives, and follow-up techniques on response to a mailed questionnaire. American Journal of Epidemiology 1998;148(10):1007-11. - PubMed
Hopkins 1983 {published data only}
    1. Hopkins K, Podolak J. Class-of-mail and the effects of monetary gratuity on the response rates of mailed questionnaires. Journal of Experimental Education 1983;51(4):169-70.
Hughes 1989 {published and unpublished data}
    1. Hughes JFR. Free reprints to increase the return of follow-up questionnaires. In: Abstracts from the Tenth Meeting of the Society of Clinical Trials, 1989 May 15-18; Minneapolis. Vol. 10. 1989:316-54.
Hunter 2018 {published data only}
    1. Hunter RF, Murray JM, Gough A, Tang J, Patterson C, French DP, et al. Effectiveness and cost-effectiveness of a loyalty scheme for physical activity behaviour change maintenance: results from a cluster randomised controlled trial. International Journal of Behavioral Nutrition and Physical Activity 2018;15(1):127. [DOI: 10.1186/s12966-018-0758-1] - DOI - PMC - PubMed
Iglesias 2000 {published data only}
    1. Iglesias C, Torgerson D. Does length of questionnaire matter? A randomised trial of response rates to a mailed questionnaire. Journal of Health Services Research & Policy 2000;5(4):219-21. - PubMed
Iglesias 2001 {published data only}
    1. Iglesias CP, Birks YF, Torgerson DJ. Improving the measurement of quality of life in older people: the York SF-12. QJM: an International Journal of Medicine 2001;94:695-8. - PubMed
Johnson 2004 {published data only}
    1. Johnson G, Oxman M, Schmader K, Levin M, Concato J, Williams H, et al. Use of an automated telephone response system for follow-up in a long-term multi-centre clinical trial. Clinical Trials 2004;2:211.
Juraskova 2014 {published data only}
    1. Juraskova I, Butow P, Bonner C, Bell ML, Smith AN, Seccombe M, et al. Improving decision making about clinical trial participation - a randomised controlled trial of a decision aid for women considering participation in the IBIS-II breast cancer prevention trial. British Journal of Cancer 2014;111(1):1-7. [DOI: 10.1038/bjc.2014.144] - DOI - PMC - PubMed
Karras‐Jean Gilles 2019 {published data only}
    1. Karras-Jean Gilles J, Astuto J, Gjicali K, Allen LR. Sample retention in an urban context: exploring influential factors within a longitudinal randomized evaluation. American Journal of Evaluation 2019;40(2):268-90. [DOI: 10.1177/1098214017742719] - DOI
Katz 2001 {published data only}
    1. Katz K, El-Mohandes A, McNeely Johnson D, Jarrett M, Rose A, et al. Retention of low income mothers in a parenting intervention study. Journal of Community Health 2001;26(3):203-18. - PubMed
Kim 2020 {published data only}
    1. Kim M, Lee H, Kiang P, Aronowitz T, Sheldon LK, Shi L, et al. A Storytelling intervention in a mobile, web-based platform: a pilot randomized controlled trial to evaluate the preliminary effectiveness to promote human papillomavirus vaccination in Korean American college women. Health Education & Behavior 2020;47(2):258-63. [DOI: 10.1177/1090198119894589] - DOI - PMC - PubMed
Kiwanuka 2018 {published data only}
    1. Kiwanuka N, Mpendo J, Asiimwe S, Ssempiira J, Nalutaaya A, Nambuusi B, et al. A randomized trial to assess retention rates using mobile phone reminders versus physical contact tracing in a potential HIV vaccine efficacy population of fishing communities around Lake Victoria, Uganda. BMC Infectious Diseases 2018;18:591. [DOI: 10.1186/s12879-018-3475-0] - DOI - PMC - PubMed
Krammer 1986 {published data only}
    1. Kramer FM, Jeffery RW, Snell MK. Monetary incentives to improve follow-up data collection. Psychological Reports 1986;58(3):739-42. [DOI: 10.2466/pr0.1986.58.3.739] - DOI - PubMed
Kuhlmann 2017 {published data only}
    1. Kuhlmann T, Reips UD, Wienert J, Lippke S. Using visual analogue scales in ehealth: non-response effects in a lifestyle intervention. Journal of Medical Internet Research 2016;18(6):e126. [DOI: 10.2196/jmir.5271] - DOI - PMC - PubMed
Lannin 2013 {published data only}
    1. Lannin NA, Anderson C, Lim J, Paice K, Price C, Faux S, et al. Telephone follow-up was more expensive but more efficient than postal in a national stroke registry. Journal of Clinical Epidemiology 2013;66(8):896-902. [DOI: 10.1016/j.jclinepi.2013.03.005] - DOI - PubMed
Leidy 2000 {published and unpublished data}
    1. Leidy NK, Legro M, Schmier J, Zyczynski T, McHorney C, Coyne K. Does order of administration affect subject response on generic and condition-specific measures of health related quality of life? Quality of Life Research 2000;9:337.
Leigh Brown 1997 {published and unpublished data}
    1. Leigh Brown AP, Lawrie HE, Kennedy AD, Webb JA, Torgerson DJ, Grant AM. Cost effectiveness of a prize draw on response to a postal questionnaire: results of a randomised trial among orthopaedic outpatients in Edinburgh. Journal of Epidemiology and Community Health 1997;51(4):463-4. - PMC - PubMed
Leighton 2018 {published data only}
    1. Leighton PA, Brealey SD, Dias JJ. Interventions to improve retention in a surgical, clinical trial: a pragmatic, stakeholder?driven approach. Journal of Evidence-based Medicine 2018;11(1):12-9. [DOI: 10.1111/jebm.12271] - DOI - PubMed
Litchfield 2005 {published data only}
    1. Litchfield J, Freeman J, Schou H, Elsley M, Fuller R, Chubb B. Is the future for clinical trials internet-based? A cluster randomized clinical trial. Clinical Trials. 2005;1:72-9. - PubMed
Malden 2019 {published data only}
    1. Malden S, Reilly JJ, Gibson AM, Bardid F, Summerbell C, De Craemer M, et al. A feasibility cluster randomised controlled trial of a preschool obesity prevention intervention: ToyBox-Scotland. Pilot and Feasibility Studies 2019 Dec 1;5(1):128. - PMC - PubMed
McAuley 1994 {published data only}
    1. McAuley E, Courneya K, Rudolph D, Cox CL. Enhancing exercise in middle aged males and females. Preventive Medicine 1994;23:498-506. - PubMed
McBee 2009 {published data only}
    1. McBee W, Clemons T, Chew E, SanGiovanni JP. A multi-level approach for retention of participants in a long-term clinical trial. Clinical Trials 2009;6:493-524.
Munoz 2017 {published data only}
    1. Muñoz RF, Leykin Y, Barrera AZ, Brown CH, Bunge EL. The impact of phone calls on follow-up rates in an online depression prevention study. Internet interventions. 2017 Jun 1;8:10-4. - PMC - PubMed
Murray 2019 {published data only}
    1. Murray JM, French DP, Patterson CC, Kee F, Gough A, Tang J, et al. Predicting outcomes from engagement with specific components of an internet-based physical activity intervention with financial incentives: process analysis of a cluster randomized controlled trial. Journal of Medical Internet Research 2019;21(4):e11394. - PMC - PubMed
Murray 2020 {published data only}
    1. Murray JM, French DP, Kee F, Gough A, Tang J, Hunter RF. Mechanisms of physical activity behavior change in an incentive-based intervention: mediation analysis. Health Psychology 2020;39(4):281-97. [DOI: 10.1037/hea0000849] - DOI - PubMed
Nicholas 2013 {published data only}
    1. Nicholas A, Bailey JV, Stevenson F, Murray E. The Sexunzipped Trial: young people?s views of participating in an online randomized controlled trial. Journal of Medical Internet Research 2013;15(12):e276. - PMC - PubMed
Nielson 2018 {published data only}
    1. Nielson CM, Rivelli JS, Fuoco MJ, Gawlik VR, Jimenez R, Petrik AF, et al. Effectiveness of automated and live phone reminders after mailed-FIT outreach in a pilot randomized trial. Preventive Medicine Reports 2018;12:210-3. - PMC - PubMed
Novak 2019 {published data only}
    1. Novak LA, Belsher BE, Freed MC, McCutchan PK, Liu X, Evatt DP, et al. Impact of financial reimbursement on retention rates in military clinical trial research: a natural experiment within a multi-site randomized effectiveness trial with active duty service members. Contemporary Clinical Trials Communications 2019;15:100353. [DOI: 10.1016/j.conctc.2019.100353] - DOI - PMC - PubMed
Nuzzolese 2020 {published data only}
    1. Nuzzolese I, Montemurro F. Attrition in metastatic breast cancer: a metric to be reported in randomised clinical trials? Lancet Oncology 2020;21(1):21-4. [DOI: 10.1016/S1470-2045(19)30792-2] - DOI - PubMed
Parker 2019 {published data only}
    1. Parker A, Arundel C, Beard D, Bower P, Brocklehurst P, Coleman E, et al. PROMoting THE USE OF SWATs (PROMETHEUS): routinely embedding recruitment and retention interventions within randomised trials. Trials 2019;20(Suppl 1):46-7.
Paul 2011 {published data only}
    1. Paul J, Iveson T, Midgley R, Harkin A, Masterton M, Alexander L, et al. Choice of randomisation time-point in non-inferiority studies of reduced treatment duration: experience from the SCOT study. Trials 2011;12:1-2. [DOI: 10.1186/1745-6215-12-S1-A30] - DOI
Phiri 2019 {published data only}
    1. Phiri SC, Mudhune S, Prust ML, Haimbe P, Shakwelele H, Chisenga T, et al. Impact of the Umoyo mother-infant pair model on HIV-positive mothers? social support, perceived stigma and 12-month retention of their HIV-exposed infants in PMTCT care: evidence from a cluster randomized controlled trial in Zambia. Trials 2019;20(1):505. [DOI: 10.1186/s13063-019-3617-8] - DOI - PMC - PubMed
Pieper 2018 {published data only}
    1. Pieper D, Kotte N, Ober P. The effect of a voucher incentive on a survey response rate in the clinical setting: a quasi-randomized controlled trial. BMC Medical Research Methodology 2018;18(1):1-4. [DOI: 10.1186/s12874-018-0544-4] - DOI - PMC - PubMed
Poling 2006 {published data only}
    1. Poling J, Oliveto A, Petry N, Sofuoglu M, Gonsai K, Gonzalez G, et al. Six-month trial of bupropion with contingency management for cocaine dependence in a methadone-maintained population. Archives of General Psychiatry 2006;63:219-28. - PubMed
Price 2019 {published data only}
    1. Price A, Bryson H, Smith A, Mensah F, Goldfeld S. Processes for engaging and retaining women who are experiencing adversity in longitudinal health services research. BMC health services research 2019;19(1):833. [DOI: 10.1186/s12913-019-4698-5] - DOI - PMC - PubMed
Puffer 2004 {published data only}
    1. Puffer S, Porthouse J, Birks Y, Morton V, Torgerson D. Increasing response rates to postal questionnaires: a randomised trial of variations in design. Journal of Health Services Research and Policy 2004;9(4):213?7. - PubMed
Rhoades 1998 {published data only}
    1. Rhoades H, Creson D, Elk R, Schmitz J, Grabowski J. Retention, HIV risk, and illicit drug use during treatment: methadone dose and visit frequency. American Journal of Public Health 1998;88(1):34-9. - PMC - PubMed
Roberts 2000 {published data only}
    1. Roberts P, Roberts C, Sibbald B, Torgerson D. The effect of a direct payment or a lottery on questionnaire response rates: a randomised controlled trial. Journal of Epidemiology and Community Health 2000;54:71-2. - PMC - PubMed
Rodgers 2019a {published data only}
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Rodgers 2019b {published data only}
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Sano 2013 {published data only}
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Smith 2015 {published data only}
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Tariq 2019 {published data only}
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References to studies awaiting assessment

Letley 2000 {published data only}
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Sutherland 1996 {published data only}
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References to ongoing studies

SWAT #100 {unpublished data only}
    1. O'Neill L, Knapp P, Doyle S, Guinan E, Hussey J. SWAT 100: Patient and family co-developed participant information to improve recruitment rates, retention, and patient understanding of a randomised trial. https://www.qub.ac.uk/sites/TheNorthernIrelandNetworkforTrialsMethodolog.... - PMC - PubMed
SWAT #105 {unpublished data only}
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SWAT #107 {unpublished data only}
    1. Shiely F. SWAT 107: Effects of a multi-trial programmable animation platform on the efficiency and success of pre-screening and subsequent recruitment to a randomised trial. https://www.qub.ac.uk/sites/TheNorthernIrelandNetworkforTrialsMethodolog....
SWAT #109 {unpublished data only}
    1. Parker A, Brealey S, Sharma HK, Welch C, Keding A, Flett L, Hunkins D, Witts J, McDaid C. SWAT 109: The effectiveness of a text message reminder which participants can respond to, compared with a?no reply? text message on questionnaire response rates. https://www.qub.ac.uk/sites/TheNorthernIrelandNetworkforTrialsMethodolog....
SWAT#110 {unpublished data only}
    1. Ooms A. SWAT 110: Printing the primary outcomE on Pink PapER versus standard paper to increase participant engagement to postal questionnaires (PEPPER). https://www.qub.ac.uk/sites/TheNorthernIrelandNetworkforTrialsMethodolog....
SWAT#112 {unpublished data only}
    1. Woodford J & von Essen L. SWAT 112: Effects on recruitment of a personalised compared with a standard study invitation letter. https://www.qub.ac.uk/sites/TheNorthernIrelandNetworkforTrialsMethodolog....
SWAT #119 {unpublished data only}
    1. Arundel C, Chetter I, Fairhurst C, Joshi K, McCaffery J, Mott A, Wilkinson J. SWAT 119: Effects on retention of giving trial participants a thank you card following each study visit.. https://www.qub.ac.uk/sites/TheNorthernIrelandNetworkforTrialsMethodolog....
SWAT #121 {unpublished data only}
    1. Dhanjal G. SWAT 121: What are the effects on retention and follow-up of courtesy telephone calls versus postcards to trial participants following enrolment? https://www.qub.ac.uk/sites/TheNorthernIrelandNetworkforTrialsMethodolog....
SWAT #51 {unpublished data only}
    1. Agus A. SWAT 51: Promoting group identity to improve questionnaire return rate. https://www.qub.ac.uk/sites/TheNorthernIrelandNetworkforTrialsMethodolog....
SWAT #54 {unpublished data only}
    1. Anand R. SWAT 54: Giving trial participants a thank you note or card after each study visit. https://www.qub.ac.uk/sites/TheNorthernIrelandNetworkforTrialsMethodolog....
SWAT #63 {unpublished data only}
    1. Azuara-Blanco A & Clarke M. SWAT 63: Does local radio and social media advertisement increase recruitment? https://www.qub.ac.uk/sites/TheNorthernIrelandNetworkforTrialsMethodolog....
SWAT #79 {unpublished data only}
    1. Backhouse M, Torgerson D, Parker A, Cockayne S. SWAT 79: Effect of birthday cards with or without nudge on retention and data completion rates in trials involving children. https://www.qub.ac.uk/sites/TheNorthernIrelandNetworkforTrialsMethodolog....
SWAT #81 {unpublished data only}
    1. BenSaaud A, Tawfick W, Jordan F. SWAT 81: A Telephone Reminder to Enhance Adherence to Interventions in Randomised Trials. https://www.qub.ac.uk/sites/TheNorthernIrelandNetworkforTrialsMethodolog.... - PubMed
SWAT #82 {published data only}
    1. Treweek S, Gillies K, Innes K, MacLennan G. SWAT 82: Sending Christmas cards to trial participants to improve retention.. https://www.qub.ac.uk/sites/TheNorthernIrelandNetworkforTrialsMethodolog.... - PMC - PubMed
SWAT #86 {unpublished data only}
    1. Sutton C, Cotterill S, Forshaw, D Rhodes S, Hammond A. SWAT 86: Advance notification of trial participants before outcome data collection to improve retention. https://www.qub.ac.uk/sites/TheNorthernIrelandNetworkforTrialsMethodolog....
SWAT #87 {unpublished data only}
    1. Hopewell S, Cureton L, Greenall G. SWAT 87: Do participants complete the original or the reminder postal follow up questionnaire? https://www.qub.ac.uk/sites/TheNorthernIrelandNetworkforTrialsMethodolog....
SWAT #89 {unpublished data only}
    1. Starr K, McRae D, Gillies K, Cooper C, Wolfe A. SWAT 89: Including a theoretically informed leaflet in a participant takehome pack of questionnaires to increase response rate. https://www.qub.ac.uk/sites/TheNorthernIrelandNetworkforTrialsMethodolog....
SWAT #92 {unpublished data only}
    1. Tew G, Tilbrook H, Paul S, Howe L, Parker A, Bell K. SWAT 92: Pen incentive to enhance retention in a randomised trial. https://www.qub.ac.uk/sites/TheNorthernIrelandNetworkforTrialsMethodolog....
SWAT #97 {unpublished data only}
    1. kKnapp P. SWAT 97: TRECA (TRials Engagement in Children and Adolescents). https://www.qub.ac.uk/sites/TheNorthernIrelandNetworkforTrialsMethodolog....

Additional references

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References to other published versions of this review

Brueton 2011
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