Successfully recruiting the pre-specified number of patients to time and target is a commonly encountered challenge that negatively impacts all stakeholders. Consequently there is a drive in research aimed at addressing trial recruitment. However, the volume of research in this area needs to be managed in an efficient way that enables trialists to access and use relevant research as well as allowing trials methodologists to identify any gaps in the research.

ORRCA aims to collate relevant methodological research on recruitment in a searchable database.


ORRCA was initiated by members of the HTMR Recruitment Working Group. The group is identifying the most effective and efficient strategies for recruitment to trials, with methodology studies inside and outside the Hubs. It facilitates networking and collaborative research across the Hubs to improve trial recruitment, and collaborates with the UKCRC Registered CTU Network to implement, evaluate and use recruitment interventions across clinical trials in the UK and beyond. 

Search strategy and review process

A search of the Cochrane Library, MEDLINE (Ovid), SCOPUS, ERIC and SCI-EXPANDED and SSCI (via ISI Web of Science) was conducted in 2015 to identify relevant studies which may inform recruitment research and strategies. To date 68,941 articles have been screened by title and abstract which has identified over 6000 articles for full text review.

A team of reviewers from the MRC HTMR recruitment working group and the HRB Trial Methodology Research network in Ireland are currently reviewing full text articles for eligibility and categorising articles according to recruitment research domains:

Articles have also been categorised according to the following types of evidence:

Randomised Evaluation – The formal assessment of the effectiveness of a recruitment strategy through a nested randomised control trial.

Non-randomised Evaluation - A comparative evaluation of a recruitment strategy such as a case control study or pre/post test. (NB this has only been applied from 2017 publications onwards)

Application - Information on the use of a recruitment strategy without comparative evaluation. This includes studies reportig the use of a strategy and hypothetical models of strategies.  

Observation - Concepts, observations or information that may be used to develop recruitment strategies. This includes lessons learnt from trials and reasons for participation/ non participation.

Additional information has been extracted from articles to allow users to search for articles based on the methods, outcomes and approach of the recruitment research, as well as the recruitment context (recruitment setting, gender, age, intervention type etc.)

Further information on the review process and how to use the site can be accessed via the HTMR webinar conducted in December 2016.


ORRCA Progress

The update of 2017 publications is now complete and the 2018 update will start shortly. 

ORRCA2, a review of the retention literature upto 2017 is nearly complete. 595 articles were added to the database at the beginning of October and more will be added on a weekly basis until the review is completed later this year.

Changes to the recruitment domains roadmap were applied during the update. A summary of changes are available along with the previous version.