Subject Recruitment

Subjects, Subjects & Subjects

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Subject recruitment problems


It has been reported that around 80% of clinical investigators fail to reach the anticipated recruitment rate and 30% do not recruit a single subject in industry-sponsored clinical trials. Those figures have not improved over the past two decades. Patient recruitment is the single most important issue that continuously fails in clinical trials. The reasons for the disappointing numbers are different between site to site, country to country, and disease to disease.

It is, however, clear that both sponsors/CROs and investigators overestimate the subject recruitment rates at 80% of all sites. A poor recruitment rate causes tension and frustration between the sponsor/CRO and the investigator, since the sponsor/CRO expects the investigator to meet the target for the number of subjects as promised during the planning stage.

Subject drop out normally occurs at different stages of a clinical trial, more precisely: (1) at subject screening, where the subject is not eligible to be included in the trial, (2) or an eligible subject refuses to participate, and (3) during the trial, where the subject drops out for personal reasons.

Not eligible: The proportion of the subjects that are eligible varies between protocols and diseases. Many times the protocol has very stringent inclusion and exclusion criteria. Some trials have reported that over 90% of the subjects approached have been found to be eligible, while other trials have reported very low eligibility rates, even below 20%.

Refusal: The refusal rate—including not turning up to the screening visit—has been reported to be around 30% again with a large variation between trials and sites. Refusals commonly fall into three categories: protocol-specific issues (about 1/3 of the refusals), inconvenience (about 1/3 of the refusals) and for other reasons (about 1/3 of the refusals).

Dropouts: Many trials report low dropout rate – on average around 10% - during the cause of the trial i.e. that is to say until the subject has met the primary trial outcome.

Summary: The key reasons for poor subject recruitment rate is an overestimation of the number of subjects available at the site, the trial eligibility rate, and the refusal rate to participate. The three causes for poor subject recruitment rate can be accurately assessed before a site agrees to participate in a trial. However, the dropout rate during the trial is difficult to predict in advance, since unknown factors including treatment side effects and/or poor treatment efficacy differ between patients.

Common subject recruitment methods


All methods of recruitment need to be submitted to the local ethics committee and accepted by the committee prior to the start of study.

Pre-study consent form: Any clinical investigator involved in industry-sponsored clinical trials and in other clinical research projects are strongly recommended to maintain a recruitment protocol that asks patients if they will agree ahead of time to be contacted for research. The protocol should be approved by the local ethics committee. Click here to see a sample Pre-study Consent Form: Pre-study consent

Clinics: Study investigators who are clinicians recruit their own patients. Nurses or staff working with the investigators may also approach the patients.

Colleagues: Study investigators approach their colleagues with a potential subject letter describing the study.

Public notice: Advertisements, notices, websites, and/or media are some of the main methods used to recruit subjects.

Public approached: Study investigators recruit potential subjects who are unknown to them. Examples include snowball sampling, use of social networks, direct approach to unknown people in public situations, and random dialling.

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“Aim at the ground, you'll never miss.”
Kristine Thomas

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