Table 1.

Deriving the factors affecting recruitment from facilitators and from barriers described in literature

Prescott et al. [[37]]
Barriers to participation in clinical trials: patient and clinician barriers
Barriers	Classification	Factor derived
Patient barriers
Additional demands of the randomized controlled trials (RCT) on the patient	Patient level factors	Additional trial investigations
Additional procedures, additional appointments, time pressures, venepuncture, inpatient hospital stays, discomfort from medical procedures, length of study, worry about experimentation, uncomfortable procedures, travel and travel costs, extra costs		Additional travel and extra costs
		Duration of trial and follow- up
Patient preference for a particular treatment	Patient level factors	Patients’/parents’ preference for a particular treatment
Patients not wanting to change medication, not to take placebo, not to take experimental medication, not to take any medication, patient request for a specific intervention, strong patient preference for one treatment option		Patients’/parents’ attitudes towards taking experimental medicine or placebo
Aversion to treatment choice by random allocation		Treatment choice by random allocation
Worry about uncertainty	Patient level factors	Patients’/parents’ concerns about side effects of new drug
Efficacy of treatment on offer is unproven, distrust of hospital or medicine, fear of unknown
Concerns about information and consent	Information and consent related factors	Amount and complexity of trial information provided
Amount of information provided to research participants, wording of information, complexity of information provided, different forms of information presentation: written /verbal/video, limited reading skills and English not being the primary language, clinicians’ experience, difficulty in giving information, worry about level of information required and that information may be frightening, consent procedure barrier to recruitment	Patient level factors	Clarity in presentation of trial information
	Clinical team factors	Experience and training of clinical team seeking consent
		Social and emotional dynamics of trial discussion
		Consent rate
		Language or cultural barrier
		Difficulty in approaching patents for consent
Clinician barriers
Time constraints	Clinical team factors	Clinical workload
Time pressures from usual clinical practice, time demands of recruitment and follow-up
Staffing and training	Clinical team factors	Research experience of clinical team
Lack of trained staff, no additional support, lack of research experience in clinicians, lack of available support staff		Availability of designated research team
		Availability of research staff out of hours
		Presence of designated research nurse/practitioner
Rewards and recognition	Excluded	Information available from the Chief Investigator
Economic incentives
Impact on doctor patient relationship fear of Adverse effect on doctor-patient relationship, perceived conflict in their role as clinicians and researchers	Clinical team factors	Clinician attitude to involving patients in research
Concern for patients
Concern about treatment toxicity, side effects, burden of trial for patients including travel distance and costs, reluctance to recruit severely ill patients
Problems in complying with the protocol	Clinical team factor	Clinician preference for a particular treatment
	Trial level factor	Study protocol compared to clinical practice
Campbell et al. [[38]]
Hypothesis of factors tested for association with recruitment success
Trials with complex trial design do not recruit as well as simple trials	Trial level factor	Trial design
Less well-funded trials do not recruit well	Trial level factor	Funding
Trials without dedicated trial management expertise do not recruit as well as those with trial management expertise	Trial level factor	Trial management
Trial with multidisciplinary input recruit better than those that do not have this input	Excluded	Information available from the Chief Investigator
Trials with consumer involvement recruit better than those that do not	Excluded	Information available from the Chief Investigator
Trials that have a successful pilot phase recruit better than those that do not have a pilot phase	Trial level factor	Previous feasibility assessment
		Previous pilot trial
Trials that have dedicated paid local coordinators recruit better than those that do not		Trial management
Cancer trials recruit better than non cancer trials	Trial level factor	Being a drug/cancer trial
Drug trials recruit better than non-drug trials		Being a drug/cancer trial
Trials funded through a response-mode funding have different recruitment rates to those funded through a commissioned process	Trial level factor	Funding
Reasons for delays in recruitment to the included cohort of trials
Problems with central staff, local research staff, internal problems (for example, staff)	Site level factor	Number of trained staff
	Clinical team factor	Motivation of clinical team
Local clinical arrangements, merging/reorganization of trusts, major relocation of services, department policies	Site level factor	Local clinical arrangements
Funding issues	Trial level factor	Funding
Delays in ethical clearance	Excluded	Information available from the Chief Investigator
Research and Development (R&D) delays, time delay since grant application
Delays in supply of drug/placebo	Excluded	Information available from the Chief Investigator
Adverse publicity about medical research, external problem (for example, publicity)	Trial level factor	Publicity by the trial team
		External publicity
Setting up general practitioner (GP) practices took longer than anticipated	Site level factor	Time to open up site
Simultaneous other local research projects, competing research, conflict with other trials	Site level factor	Competing local research projects
Delays due to changes in data legislation, changes in technology	Excluded	Information available from the Chief Investigator
Fewer eligible than expected, smaller percentage agreeing to participate, recruitment targets too ambitious	Trial level factor	Lack of pilot/feasibility assessment
	Site level factor	Recruitment target
Absence of perceived clinical equipoise	Trial level factor	Clinical equipoise
Issues with procedures/interventions, trial process too demanding	Patient level factor	Additional trial investigations
Complexity of trial design, trial methodology considered too complex	Trial level factor	Trial design
Conflicting workload pressures, long waiting lists, additional theatre time required	Clinical team factor	Clinical workload
Language/written English difficulties	Patient level factor	Language or cultural barrier
Treatment preferences	Patient level factor	Patients’/parents’ preference for a particular treatment
	Clinical team factor	Clinician preference for particular treatment
Research not considered as priority	Clinical team factor	Perceived importance of research generally in clinical practice
		Perceived importance of the particular research question
No local access to intervention	Patient level factor	Intervention available only in the trial
Case studies of trials: common factors in the successes of part B trials
Facilitator	Classification	Factor derived
Important/interesting research question, topic important, urgent need for research, important question, timely and managed to roll several questions into one study	Clinical team factor	Perceived importance of the particular research question
Good design/good protocol, pragmatic study	Trial level factor	Trial design
		Study protocol compared to clinical practice
Clinicians keen to recruit to trial	Clinical team factor	Motivation of clinical team
		Clinician attitude to involving patients in research
Drugs already tested, so easy to explain to patients	Patient level factor	Familiarity with experimental treatment
Did not demand extra effort from patients, Impact on practice running and costs minimized, minimizing work for health professionals	Patient level factor	Additional trial demands
No competing trials for those centers/patients	Site level factor	Competing local research projects
Drugs not available outside the trial	Patient level factor	Intervention available only in the trial
Excellent trial management, trial units helpful, caring, annual meetings for all concerned, role of trial steering group	Trial level factor	Trial management
Good planning and organization by Clinical Trials Support Unit (CTSU), CTSU responsive, efficient, central organization of many aspects of research
Good communication between trial team and clinicians, flexibility of trial teams	Study team factor	Communication and coordination among study team members at site
Good public relations/feedback/updates	Trial level factor	Trial publicity
Good funding, National Health Service (NHS) funding	Trial level factor	Funding
Trial run by good team/infrastructure, Principal Investigator (PI) well respected, PIs worked hard to keep collaborators on board, trial team communicative, responsive and alert to problems. Communication within team, between team and collaborating clinicians	Study team factors	Motivation of the study team at site
	Clinical team factor	Research experience of PI and study team members at site
Good trial team, good research assistants		Communication and coordination among study team members at site
Team worked hard at how to explain the study to patients		Communication and coordination between study team at site and Clinical Trials Unit (CTU)
		Research experience of clinical team
		Communication skills of clinical team
Role of research nurse	Clinical team factor	Presence of designated research nurse/practitioner
Study included everybody	Trial level factor	Patient inclusion criteria
Toerien et al. [[39]]
Study design, number of arms, control: active/placebo	Trial level factor	Trial design
Single/multicenter	Excluded	Information will be present
Intervention: drug/surgery/allied/others	Trial level factor	Being a drug/cancer/surgical/-----trial
Funding source	Trial level factor	Funding
Caldwell et al.[[40]]
Recruitment strategies
Novel trial designs	Trial level factor	Trial design
Recruiter differences	Information and consent related factors	Experience and training of doctors clinical team seeking consent
		Senior doctors and nurses seeking consent
Financial incentives for patients/participants	Excluded	Monetary incentives not acceptable for clinical research in United Kingdom
Methods of providing information	Information and consent related factors	Amount and complexity of information provided
	Patient level factor	Clarity in presentation of trial information
		Consent rate
Treweek et al.[[2]]
Recruitment strategies
Design changes	Trial level factor	Trial design
Modification to the consent form or process	Patient level factor	Consent rate
Modification to the approach made to potential participants	Information and consent related factors	Amount and complexity of information provided
		Clarity in presentation of trial information
		Senior doctors and nurses seeking consent
Financial incentives for patients/participants	Excluded	Monetary incentives not acceptable for clinical research in United Kingdom
Modification to the training given to recruiters	Information and consent related factors	Experience and training of clinical team seeking consent
Greater contact between trial coordinator and trial sites	Trial level factor	Trial management