Participant Recruitment

Participant Recruitment for Clinical Trials and Research Studies

Patient recruitment for clinical trials involves sponsors finding ways to connect with eligible participants that are willing to take part in the research study. Those responsible for patient recruitment must enlist a sample that is representative of the target audience. At the same time, they must ensure that there are enough participants in the study to meet sample size and power requirements to validate results.

This process is not as straightforward as it seems - a recent study found that nearly 80% of clinical studies fail to finish on time, two-thirds fail to meet patient enrollment and 85% fail to retain enough patients1.

Difficulties with patient recruitment for clinical trials and research studies can disrupt research timetables, cause additional burden to staff and administrators, and eventually cause a trial to be abandoned altogether. 

To conduct successful studies, trial sponsors must find new ways to overcome patient recruitment challenges. These may include exploring different methods of reaching participants, building a pipeline of potential candidates, or finding a recruitment management partner to help increase response, eliminate delays, and ensure the success of the clinical trial.

Challenges of Patient Recruitment

Patient recruitment is challenging for various reasons, including Sample Size, Lasagna’s Law, Selection Bias, and Retention. 

Sample Size

Correctly estimating sample size is critical to the eventual success of a clinical trial or study. A sample size that is too small can lead to irrelevant attributions, misleading results, or Type II errors; one that is too large is a waste of time and resources. 

Lasagna’s Law

Lasagna’s Law postulates that the number of potential participants is drastically overestimated ahead of a trial, leading to a disconnect between expectation and reality. For example, the original study described a trial in which the sponsors estimated 8,000 potential participants, of which only 100 were actually eligible2.

Selection Bias

The selection bias issue relates to the diversity of eligible participants who agree to take part in the study. During recruitment, the total audience of people reached can self-select by deciding not to take part in the study. This results in a biased candidate pool, as the people that agree to enter the study may skew toward a specific demographic type. Some characteristics of people who tend not to participate in trials or studies include:

  • Older
  • Male
  • Urban resident
  • Health issues


Most studies are not completed in a single visit. Instead, they require multiple check-ins, visits, and follow-up appointments. This means that participant retention is critical to ensure that researchers can complete the study and results are meaningful. When participants drop out after enrollment, it is expensive in terms of time and resources. Building relationships with participants from the start and employing retention strategies is essential in patient recruitment, as is planning for a certain amount of attrition.

Patient Recruitment Approaches

Each study or trial should have an approach that best suits the question being asked. Possible approaches to patient recruitment include:

All at once: participants are recruited together and begin the trial simultaneously

Batch mode: participants enter the trial in small groups or batches 

Continuous: participants are recruited on an ongoing basis, beginning and progressing through the trial individually until the desired number is reached

Date-based: participants are recruited on an ongoing basis, moving through the trial until a fixed date is reached.

Patient Recruitment Strategies

Patient recruitment for clinical trials has traditionally occurred through posters or direct communications with patients in doctor’s offices, hospitals, or healthcare clinics. However, technology has created a variety of new interaction methods and channels for disseminating information - these can all be applied to patient recruitment efforts.

Traditional Advertising

Physical posters or brochures placed where the target audience can access them are one way to reach candidates for clinical trials. When using this type of advertising, it is vital to ensure that the messaging is compelling enough to elicit a response from the audience without crossing any ethical boundaries.

Doctor-Patient Contact

A clinical trial or study often involves people who have experienced, or are interested in, a specific medical condition. This makes contacting potential participants through a healthcare provider a common choice for clinical trials.

A recent study found that 68% of doctors were willing to refer patients but had not because they lacked complete information for a study3. This suggests that researchers could get more participants through patient referrals if they improve their communications.

Social Media

Social media platforms have created new ways for people to connect in their work and home lives. It has also opened up many new methods for researchers to communicate with potential participants in clinical trials. 

Social media can be a more robust choice than traditional recruitment channels. Through social media, researchers can provide detailed information that they control; and set up feedback to gain greater insight into what potential recruits are thinking and feeling.

Patient Recruitment Companies

Partnering with a patient recruitment company can be a cost-effective, easy-to-manage, structured method of recruiting participants for clinical trials and studies. Researchers benefit from gaining access to a population of interested participants they may not otherwise have reached. Additionally, some partner companies offer digital marketing support and expertise to improve the efficiency and effectiveness of patient recruitment efforts.

Research & Me offers academic, corporate medical and pharmaceutical researchers the ability to publish their clinical trials and research studies for free, with access to over 10,000 candidates. Additionally, the Research & Me Marketplace offers outreach, digital marketing, data analytics, and reporting services for trials and studies where qualifying participants are more difficult to recruit


(1) Clinical Leader; Considerations for Improving Patient Recruitment Into Clinical Trials

(2) NIH; Problems in Publication of Clinical Trial Methodology

(3) Outsourcing-Pharma; Physicians Report Referring Patients to Clinical Trials, Sponsors Assume They Don't

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