Post-trial follow-up methodology in large randomized controlled trials: a systematic review protocol
© The Author(s). 2016
Received: 17 August 2016
Accepted: 29 November 2016
Published: 15 December 2016
Clinical trials typically have a relatively short follow-up period, and may both underestimate potential benefits of treatments investigated, and fail to detect hazards, which can take much longer to emerge. Prolonged follow-up of trial participants after the end of the scheduled trial period can provide important information on both efficacy and safety outcomes. This protocol describes a systematic review to qualitatively compare methods of post-trial follow-up used in large randomized controlled trials.
A systematic search of electronic databases and clinical trial registries will use a predefined search strategy. All large (more than 1000 adult participants) randomized controlled trials will be evaluated. Two reviewers will screen and extract data according to this protocol with the aim of 95% concordance of papers checked and discrepancies will be resolved by a third reviewer. Trial methods, participant retention rates and prevalence of missing data will be recorded and compared. The potential for bias will be evaluated using the Cochrane Risk of Bias tool (applied to the methods used during the in-trial period) with the aim of investigating whether the quality of the post-trial follow-up methodology might be predicted by the quality of the methods used for the original trial.
Post-trial follow-up can provide valuable information about the long-term benefits and hazards of medical interventions. However, it can be logistically challenging and costly. The aim of this systematic review is to describe how trial participants have been followed-up post-trial in order to inform future post-trial follow-up designs.
Systematic review registration
Not applicable for PROSPERO registration.
KeywordsMethodology Post-trial Retention Randomized controlled trial Long term Cost Follow-up Effective
Randomized controlled trials (RCTs) are considered to be the gold standard for assessing the effects of a treatment. However, RCTs are costly and usually involve a relatively brief treatment period with limited follow-up. A treatment response restricted to this brief “in-trial” period can potentially underestimate the long-term benefits of treatment and also may fail to detect delayed hazards.
Post-trial follow-up (PTFU) is defined here as extended follow-up which starts after the end of the scheduled period of the original trial. Longer term follow-up of trial participants is important as persistent effects may be detected years later after treatment cessation  or even enhanced benefits observed decades later—a so-called “legacy-effect” . Furthermore, delayed hazards may only emerge several years after exposure to certain treatments. Therefore, PTFU may add significant scientific value to the evaluation of many healthcare interventions.
There is a wide literature describing the importance of completeness of follow-up during the in-trial period of a RCT, without which the unbiased ascertainment of outcomes may be compromised and statistical power considerably reduced . Many strategies to enhance follow-up during RCTs have been investigated and this remains an area of much ongoing research . Without high quality in-trial follow-up, the value of post-trial follow-up will be extremely limited.
By contrast, little research has been done to evaluate methods for PTFU. Face-to-face follow-up is widely used during the initial "in-trial" period, but is costly if employed longer term. Telephone-based approaches are more practical, with the ability to contact many participants coordinated by a central trial office, and postal follow-up has been shown to be effective . Web-based techniques may become more widespread as technological advances develop .
The use of routine health records can provide detailed information relatively inexpensively , but the availability of such data and rules governing access to it varies across countries. In the UK, Health Episode Statistics (HES) are held by the Health and Social Care Information Centre (HSCIC) and can be used as a streamlined method to follow-up trial participants. These routinely collected electronic health records include diagnostic codes (ICD-10) for hospital admissions and can be supplemented with mortality records and cancer registry data.
All published, health-related RCTs which have recruited more than 1000 participants and implemented PTFU are to be included in this systematic review. The RCT must have reached its scheduled end before PTFU commenced. Only studies published between 2006 and 2016 will be included.
Selection criteria of published articles eligible for systematic review
• Large (>1000 participants) randomized controlled trials only
• Randomized controlled trials in adult humans
• Any type of methodology used for post-trial follow-up
• Healthcare intervention for the purpose of treatment
• Published articles
(a) Publication type
• Narrative reviews
• Unpublished manuscripts
• Government reports
• Books and book chapters
• Conference proceedings
• Lectures and addresses
• Consensus development statements (including guideline statements)
(b) Study design
• Non-randomized studies
(c) Study population
Trials including participants aged over 18 years old are eligible.
Methods and incentives (monetary or by other means) used for post-trial follow-up including direct “face-to-face” follow-up and indirect follow-up, eg, medical record review, telephone and postal follow-up, and electronic follow-up including access to electronic health records will be included.
Methodology used to follow up participants’ post trial will be compared qualitatively in a table format.
Included studies must have published the total number of participants followed-up compared to the total number alive at the end of the in-trial period to calculate retention rates. Where available, secondary outcome measures of cost, incentives used for follow-up, and cost-effectiveness will be recorded and assessed. If there are missing data, an attempt to contact the study authors will be made. Further exploratory comparisons will be made depending on the information available (for example, describing the use of different approaches according to context, such as regional variations or comparisons of industry-funded trials versus those funded through other sources).
Only studies published in English will be included.
Cochrane methodology group register
Cochrane Central Register of Controlled Trials (CENTRAL)
Trials registry: Clinical-trials.gov (http://clinicaltrials.gov/)
Screening for eligible studies
Data collection and analysis
Data extraction and management
Assessing the quality of the post-trial follow-up methodology
In order to investigate whether the quality of the post-trial follow-up methodology might be predicted by the quality of the methods used for the original trial, risk of bias will be assessed in those trials chosen for data extraction using the Cochrane Risk of Bias tool. The tool will be applied to the methods used in the main trial, (not the PTFU) focusing on incomplete data; outcome reporting; for-profit bias and other bias sources. Two reviewers will independently assess the risk of bias, and disagreements will be resolved by a third reviewer. The assessment of bias results will be taken into account as part of the assessment of quality of the PTFU methods used.
Presenting and reporting of results
The Preferred Reporting Items for Systematic Review Protocols (PRISMA-P)  will be followed, including a PRISMA diagram to illustrate the process of selecting eligible studies (Fig. 1). Using the PRISMA guidelines (Additional file 1), the results of this review will be presented and the outcomes tabulated with respect to the different methodologies used in a qualitative and comparative style.
Interpretation of findings
The findings of this review will be discussed and potential limitations considered.
Large randomized trials are essential for determining the magnitude of the effects of an intervention. Post-trial follow-up of large RCTs is important, not only for defining the effect of an intervention long-term but also for ascertaining the safety profile and potential hazards which might not be apparent during the relatively brief in-trial period. However, randomized trials can be very expensive, and funding is limited, hence streamlined and effective methodology for PTFU is desirable. This systematic review aims to inform the design of post-trial follow-up for a wide range of randomized trials.
Cochrane Central Register of Controlled Trials
Excerpta Medica database
Grading of Recommendations Assessment, Development and Evaluation
Health Episode Statistics
Health and Social Care Information Centre
International Classification of Diseases codes
Preferred Reporting Items for Systematic Review Protocols
Randomized controlled trial
Many thanks to Danielle Edwards (Clinical Trial Service Unit, University of Oxford) who advised on the figures for publication and Nia Roberts (Bodelian libraries, University of Oxford) who advised on the search strategy.
RLB has received funding from the Royal College of Surgeons of England Research Fellowship.
Availability of data and materials
Data sharing is not applicable to this article as no datasets were generated or analyzed during the current study.
RLB designed the protocol. RLB, LB, and RB drafted the protocol. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
Consent for publication
RLB, LB, and RB consent for publication.
Ethics approval and consent to participate
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
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