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Table 2 Reasons for recruitment failure obtained from interviews and journal publications

From: Exploring reasons for recruitment failure in clinical trials: a qualitative study with clinical trial stakeholders in Switzerland, Germany, and Canada

Reported reasons Frequency (from interviews n = 49) a Frequency (from publications n = 131) g [4]
 Initial funding insufficient (including lack of funding for planning; inadequate financial planning) 10 15
 Additional funding for recruitment escalation/prolongation unavailable 1 6
Initial funding withdrawn when slow recruitment became apparent 0 4
Research environment-related   
 Delay in opening recruitment sites (e.g., delayed ethical approval, new regulatory acts) 8 7
 High bureaucratic burden for clinical researchers (e.g., GCP regulations) 2 3
Patients not seeking trials in high-quality health care system with many options (lack of incentive) 6 0
Decentralized health care system with many small hospitals and few referrals in Switzerland (e.g., because of restrictive regional insurance contracts; in Germany peripheral hospitals often provide specialized care and refer only severely ill patients to tertiary care hospitals) 4 0
 General mistrust in research (unbalanced views in media, no public figures as role model to encourage trial participation) 3 4
 Concurrent competing trials (particularly if other trial in same patient population pays more—see below “Financial conflicts of interest”) 6 11
 New evidence from other study about effectiveness of trial intervention (e.g., change of standard care during prolonged trial)—affects “equipoise” for recruiters and participants (see below) 4 28
Design-related b   
Research question insufficiently compelling (e.g., perceived as little relevant for patients and the scientific community) 5 0
 Low prevalence of condition of interest (seasonal effects, rare diseases) 7 2
 Too narrow eligibility criteria 12 59
 Overoptimistic/unreliable recruitment estimates c (e.g., no pilot study; no empirical data; insufficient feasibility checking; weak commitment from centers) 26 10
Too few recruiting sites planned or too few study staff (e.g., recruiters, limited engagement of study nurses) 7 0
 Recruitment insufficiently compatible with routine clinical practice (e.g., urgent transfers from intensive care, different treatment availabilities at different centers or at weekends, referrals too late to tertiary care) d 7 11
 Lack of methodological/logistical support (e.g., from contract research organization, or clinical trial unit) 4 7
 Trial design too difficult to explain or implement (e.g., complex interventions, factorial design) 7 4
Unclear eligibility criteria or enrolment process (e.g., regarding timing of randomization or responsibilities of involved investigators/personnel) 0 6
Ineffective screening/advertising strategy (e.g., email instead of phone call, newspaper campaign only) 0 5
Patients approached in inconvenient situation (e.g., women in labor, patients in ICU) 0 5
Lack of patient engagement in trial design/planning 4 0
Trial team/recruiter-related   
 Lack of equipoise e 4 34
 High administrative burden/time constraints/other priorities 4 11
 Lack of incentive (e.g., financial, academic recognition, career advancement) 2 4
 Lack of engagement/cooperation (e.g., recruiters (practicing clinicians) unaware of trial, recruiters not involved with study team, departments not referring patients to trial recruiters) 12 4
Lack of competence/training/experience (includes inadequate planning; “enthusiasm is not enough,” staff turnover) 11 0
“Trial fatigue” (motivation compromised due to recurrent prolongation of recruitment period) 3 0
 Financial conflict of interest (e.g., trial results favoring conservative treatment over surgery may lead to less earnings; other trial in same patient population pays more—see above “Concurrent competing trials”) 2 1
 Lack of equipoise f 6 40
 High burden (e.g., many visits, invasive procedure/biopsies, long questionnaires, costs) 9 20
 Language or cultural barriers 1 4
Lack of financial incentive 0 2
Lack of encouragement from patient support organizations 0 1
Lack of trust due to short -term relationship with healthcare team (e.g., acute care vs chronic conditions (e.g., dialysis patients)) 2 0
  1. Reasons identified in interviews only are marked in bold and those identified in published reports only are marked in cursory font
  2. aWe obtained 179 accounts of explanations for poor participant recruitment from 49 qualitative interviews. These explanations could be classified into 29 reasons. If a respondent described more than one possible factor (explained in parenthesis) that contributed to the same reason, it was counted only once
  3. bNeed for simpler/more pragmatic design
  4. cReasons for “overoptimism”: intention to convince reviewers of trial feasibility in case of a grant proposal/ethics review or when applying for participation in an industry trial
  5. dRequirement of intensified cooperation/communication among research team or intensified training of recruiters
  6. eEquipoise means the uncertainty about benefits and harms of an intervention or about the superiority of one intervention over another, and is a pre-requisite for randomization. Lack of equipoise was reported as concerns about disadvantages for participants, vulnerable populations (e.g., children), trial questioning current practice, loss of professional autonomy, dislike of randomization to unwanted intervention, worry about doctor-patient relationship, recommendations from opinion leaders, media information favoring a particular treatment, and inadvertent use of unbalanced terminology such as gold standard
  7. fEquipoise means the uncertainty about benefits and harms of an intervention or about the superiority of one intervention over another, and is a pre-requisite for randomization. Lack of equipoise was reported as influenced by next of kin or caring physician, concerns regarding side effects or potential diagnosis, vulnerable populations (e.g., children), concerns regarding randomization to unwanted intervention, unwillingness to receive placebo or no treatment, loss of personal autonomy/reluctance to become a “guinea pig,” worry about doctor-patient relationship, and media information favoring a particular treatment
  8. gMost publications mentioned more than one reason