Is the Study Feasible With the Participants You Can Realistically Reach?

Can You Actually Reach the People Your Study Requires?

Your research question may identify exactly the population you need: secondary-school teachers using a particular technology, patients with a relatively uncommon condition, first-generation university students, senior administrators, or participants who must be followed for several years.

Defining that population is the easy part. Recruiting it may be another matter entirely.

The people may exist but be difficult to identify. Institutions may control access to them. Eligibility criteria may eliminate most volunteers. Potential participants may have little reason to participate, substantial reasons not to, or too little time for what your protocol requires. Even successful enrollment does not guarantee that enough participants will remain through follow-up.

Participant recruitment is consequently treated as a central component of study feasibility in feasibility-study guidance and clinical-trial feasibility assessments. The relevant question is not merely whether the target population exists, but whether the study has a credible pathway for recruiting and retaining the people needed to generate adequate evidence.

Participant Feasibility Requires More Than an Eligible Population

How Do You Know Whether Participant Recruitment Is Realistically Feasible?

Participant feasibility is sometimes reduced to a sample-size calculation. The calculation tells you how many observations a particular analysis may require under specified assumptions. It does not tell you whether those observations can actually be obtained.

A more realistic assessment works backward from the required participants through the recruitment process. Who is eligible? How many can you identify? How many can you contact? How many are likely to respond? How many will consent? How many will complete the relevant procedures? If follow-up is required, how many are likely to remain?

Distinguish the Target Population From the Accessible Population

Your target population is the population about which you ultimately want to make claims. Your accessible population is the portion you can realistically approach through the institutions, communities, databases, professional networks, clinics, schools, platforms, or other recruitment channels available to you.

A study becomes vulnerable when these are quietly treated as equivalent. Recruiting students from one accessible university does not automatically make them representative of all university students. Recruiting people who respond to an online advertisement may systematically favor those who notice the advertisement, have internet access, or are particularly interested in the subject.

Accessibility is necessary for feasibility, but the accessible sample must also remain relevant to the question you claim to answer.

Map the Entire Recruitment Funnel

Suppose you need 300 completed responses. Finding a mailing list containing 300 names does not make recruitment feasible.

Some people may be ineligible. Some contact details may be outdated. Many may ignore the invitation. Others may begin but not complete the study. If the study has multiple sessions, further losses may occur between enrollment and final assessment.

Feasibility guidance recommends tracking quantities such as the numbers screened, eligible, consented, enrolled, and retained, along with reasons for non-recruitment and the performance of recruitment strategies. These quantities reveal where the recruitment pathway is likely to lose participants.

Estimate each stage using evidence where possible. Previous studies in comparable populations, institutional records, preliminary screening, pilot recruitment, or prior experience from the research setting may be more informative than optimistic assumptions.

Verify Gatekeeper Access Before Treating Participants as Available

Researchers frequently describe participants as “accessible” because they work or study at a particular institution. Yet access may depend on approval from school administrators, hospital departments, community organizations, employers, platform owners, professional associations, or other gatekeepers.

Ethics approval and site access are also different permissions. An ethics committee may approve a protocol without giving you the institutional authority to recruit at a particular site.

If the design depends on one organization, obtain realistic information about its willingness and ability to facilitate recruitment before making the study contingent on that access.

Eligibility Criteria Can Make a Large Population Very Small

Each inclusion criterion narrows the pool. A study may require participants who teach a particular course, have used a technology for six months, work full-time, belong to a specific professional group, and are available for repeated interviews. Thousands of employees in the organization may eventually produce only dozens of eligible individuals.

Eligibility criteria should protect the logic and validity of the study, not simply maximize recruitment. Still, examine whether every restriction is necessary. Unnecessary criteria can make recruitment difficult while also narrowing the population to which the findings apply.

Willingness to Participate Is Part of Feasibility

Eligibility does not imply willingness.

Participation may require time, travel, disclosure of sensitive information, repeated assessments, unfamiliar technology, physical procedures, or interaction with researchers on topics participants would rather avoid. Recruitment strategies can also influence who participates and how many eligible participants are obtained.

Ask what participation looks like from the participant's side. A protocol that appears modest to a researcher may be burdensome to a teacher during examinations, a patient undergoing treatment, or an employee being asked about workplace practices.

This connects participant feasibility directly to whether participant burden is proportionate to the likely value of the knowledge.

Recruitment Rate Matters as Much as the Final Sample Size

A study requiring 500 participants may be feasible if a large eligible population can be recruited rapidly. A study requiring only 30 may be infeasible if the population is rare and only one eligible participant appears each month.

Estimate recruitment as a rate: eligible and enrolled participants per site, per recruitment channel, or per unit of time. Then compare that rate with your project timeline.

Recruitment and retention planning before a full trial is particularly important because failure to reach the intended sample can undermine planned analyses and the strength of resulting conclusions.

Retention Matters When Participants Must Stay

Cross-sectional studies may require one completed interaction. Longitudinal research, repeated-measures designs, interventions, cohort studies, and multi-session qualitative projects may require participants to remain engaged over weeks, months, or years.

If 200 participants must complete the final follow-up, recruiting exactly 200 at baseline assumes zero attrition. That is rarely a sensible planning assumption.

Estimate retention using comparable evidence where available. More importantly, ask whether dropout could be systematic. If participants with particular experiences or characteristics are more likely to leave, attrition may affect more than sample size. It may change the composition of the evidence.

More Recruitment Channels Are Not Automatically Better

Researchers may respond to recruitment difficulty by opening every available channel: email lists, social media, classrooms, advertisements, professional groups, community organizations, and participant referrals.

This can improve numbers, but recruitment methods can yield participants with different characteristics. Feasibility guidance notes that recruitment strategies may affect both the number and demographic composition of participants obtained.

Recruitment strategy is therefore part of sampling logic. Ask not only, “Will this get me enough people?” but also, “Who is this method likely to bring into the study, and who might it systematically miss?”

Do Not Solve Recruitment Problems by Quietly Changing the Population

Suppose your question concerns experienced special-education teachers, but recruitment proves difficult. Opening participation to all teachers may quickly increase enrollment. It also changes the population and possibly the research question.

Sometimes broadening eligibility is defensible. If so, revise the question, sampling rationale, analysis, and intended claims accordingly. Do not retain the original population in the title and discussion while collecting evidence from whoever was easiest to recruit.

Feasibility Work May Be Necessary When Recruitment Assumptions Are Uncertain

If the study depends on uncertain recruitment pathways, preliminary feasibility work can test whether participants can actually be identified, recruited, and retained. Feasibility studies are explicitly used to examine recruitment strategies and other processes before researchers commit to larger evaluations.

The objective is not to pretend that a small pilot has answered the substantive research question. It is to learn whether the machinery required to answer that question can work.

When a Large Population Produces Too Few Realistic Participants

The important denominator was never “2,000 faculty members.” It was the much smaller number who were eligible, reachable, willing, and likely to provide the complete evidence the design required.

What Makes Participant Access Look Easier Than It Is?

Build a Recruitment Funnel Before You Build the Final Protocol

Write down the number of participants required at the point where they contribute usable evidence. Then work backward through expected completion, retention, consent, eligibility, response, contact, and initial pool size.

Mark every conversion rate that is based on evidence and every rate that is merely assumed. The second category deserves attention before the study begins.

Participant access is only one feasibility dimension. Even with an excellent recruitment pathway, you still need to determine whether the required data can realistically be obtained, whether the project fits the available time, and whether the necessary expertise and resources are in place.

Can You Recruit the Participants the Study Actually Needs?

Questions About Participant Recruitment Feasibility

Your Real Sample Is the One You Can Recruit and Retain

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