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Optimising recruitment to a clinical trial

Optimising recruitment to a clinical trial

01 June 2022

Irene Stratton, Senior Medical Statistician, RDS South Central

During the past 2 years since the start of the COVID19 pandemic, we have seen clinical trials struggling to recruit participants. Clinics were cancelled and when they were restarted people were sometimes reluctant to come into clinics. Clinical research staff were redeployed from research to front-line services. As we look at protocols for new studies it’s important to ensure that the sample size has a good chance of being met in the planned timeframe. Many studies for which I have been on either the Trial Steering Committee or Data Monitoring Committee have struggled to recruit and some of the problems might have been avoided – especially the problem of poorly recruiting centres.

What can we do at the planning stage?

In a single centre trial, the lead investigator will have a good idea of the number of service users who will be coming through the clinic and who might be amenable to recruitment to a trial. In a multicentre trial participating centres need to give an estimate of the numbers who they might be able to recruit. It’s important that this is realistic.  An audit within each potential centre could inform decisions as to whether it should be included or not.  Some would-be collaborators are too optimistic about the numbers with a condition coming through. Discussions with the collaborating centres could also cover the availability of staff– if a research nurse is available for 3 days a week fewer than half of eligible patients might be recruited for a trial of in-patients.

What can we learn from a pilot study?

If a study is being run in a patient group which is often the target of research the proportion of those approached who consent to be screened will be known. In a study in a group that’s not often the target of research a pilot study will be useful.  A recent pilot study (1) in people with serious mental illness had a recruitment target number of 60. Over 15 months 799 people were assessed for eligibility, 448 were eligible, of these 127 could not be contacted. Of the 321 invited to a screening visit, 266 did not attend (reasons given for 105 of these), 55 attended and 47 entered the trial. The recruitment rate was just 10%.

What can we learn from the literature?

Having been involved in trials for four decades I was surprised to find that there is a sizable literature on problems with recruitment to studies. A search on PubMed with the terms “recruitment” and “trial” in the title turns up almost 900 papers. Although in no sense a formal review I have looked at the most recent 20 of these papers and they cover topics on costs of recruitment (some comparing ways of using social media), ways of accessing groups of interest, reasons for poor recruitment in people with cancer, difficulties engaging with ethnic minority groups.

How can the Research Design Service help?

I haven’t seen any references to these papers when discussing recruitment in any of the applications that I have seen coming through RDS in the past year and now I will be looking to change this.  If anyone is interested in my Excel spreadsheet of papers do get in touch! Do also get in touch with your local RDS for our free and confidential advice and support on recruitment strategies for clinical trials or, indeed, any health or social care research funding application.


      1. The use of liraglutide 3.0 mg daily in the management of overweight and obesity in people with schizophrenia, schizoaffective disorder and first episode psychosis: Results of a pilot randomized, double-blind, placebo-controlled trial. Clare A Whicher, Hermione C Price, Peter Phiri, Shanaya Rathod, Katharine Barnard-Kelly, Kandala Ngianga, Kerensa Thorne, Carolyn Asher, Robert C Peveler, Joanne McCarthy, Richard I G Holt
        Diabetes Obes Metab 2021 Jun;23(6):1262-1271


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