How Do You Decide Whether Recruitment Is Feasible Before Committing to the Main Study?

How Can You Know Whether Your Recruitment Plan Will Actually Deliver the Sample?

Your sample-size calculation says you need 300 participants. Your recruitment plan says you will approach students, patients, teachers, employees, households, or another target population until you reach 300.

There is an important gap between those two statements.

How many potentially eligible people are actually accessible? How many satisfy the eligibility criteria? How many can be contacted? How many agree to participate? How long does each stage take? What happens if the recruitment rate slows after the easiest participants have been enrolled?

Recruitment feasibility is about whether the recruitment system, not merely the target number, can realistically produce the sample required by the main study within its available time, sites, population, and resources.

Test the Recruitment Pathway Against What the Main Study Requires

Recruitment Feasibility Is a Pipeline, Not a Single Percentage

Begin With the Recruitment Requirement of the Main Study

You cannot decide whether recruitment is feasible without first defining what successful recruitment would mean for the proposed study.

Suppose the main study requires 300 participants within ten months. That translates into an average of 30 participants per month if recruitment is approximately steady. If recruitment will occur at five sites, you also need to consider how many participants each site can realistically contribute and whether recruitment is expected to begin simultaneously.

The target may include more than total sample size. A study may require sufficient participants in particular age groups, settings, study arms, clusters, or other analytically important categories. Recruiting the total number while systematically missing an essential segment of the target population may not satisfy the design.

Recruitment feasibility therefore begins with explicit goals: who needs to be recruited, how many, from where, and by when.

Do Not Confuse the Target Population With the Accessible Population

A population can appear enormous on paper while the number of people you can actually recruit is much smaller.

Consider a study of university students. An institution may have 20,000 students, but perhaps only students in particular programs or year levels satisfy the eligibility criteria. Some cannot be contacted through the available channels. Others may be unavailable during the recruitment period. Still others may decline participation.

The same issue occurs in clinical, community, organizational, and school-based research. The theoretical target population is not the same as the pool that can realistically enter the study.

Before assuming recruitment is feasible, estimate the accessible population and identify the restrictions that reduce it.

Map Every Step From Identification to Enrollment

A recruitment rate calculated only from the final number enrolled can hide where the process is failing.

A more informative approach tracks the pathway. Depending on the study, this might include potential participants identified, screened, eligible, approached or contacted, responding, consenting, and finally enrolled.

The exact stages depend on the design. The purpose of mapping them is to identify the denominator behind every percentage and determine where losses occur.

Calculate Rates That Answer Different Recruitment Questions

There is no single recruitment percentage that tells the whole story. Different denominators answer different questions.

These calculations answer different questions. A low eligibility rate suggests that the initial pool contains many people who cannot enter the study. A low consent rate suggests a problem after eligible participants are approached. A slow recruitment rate despite acceptable conversion percentages may indicate that too few potential participants enter the pathway in the first place.

Time Is Part of Recruitment Feasibility

“We successfully recruited 50 participants” is incomplete without knowing how long recruitment took.

If a pilot recruits 50 participants in one month and the main study requires 300 participants over twelve months under comparable conditions, the result may be encouraging. If recruiting those same 50 participants took ten months, the implications are very different.

Track the beginning and end of recruitment periods, enrollment over time, site activation where relevant, and interruptions such as academic calendars, holidays, clinic schedules, or organizational cycles that may affect availability.

Recruitment may also be nonlinear. Initial enthusiasm, intensive researcher involvement, or a readily accessible first pool can make early recruitment faster than later recruitment. Extrapolation should therefore be cautious.

Track Why Potential Participants Are Lost

A feasibility assessment becomes much more useful when it explains why recruitment falls short.

Potential participants may be lost because they do not meet eligibility criteria, cannot be contacted, decline participation, cannot accommodate the schedule, find procedures burdensome, lack required technology, or encounter other barriers.

These reasons suggest different solutions. If most losses occur because eligibility criteria exclude otherwise suitable participants, researchers may reconsider whether every criterion is scientifically necessary. If eligible people cannot be contacted, changing the outreach method may be more relevant. If participants decline because of burden, the study procedures themselves may need attention.

Systematically tracking losses converts “recruitment was difficult” into information that can improve the main study.

Recruitment Quality Can Matter as Much as Recruitment Quantity

Meeting the overall enrollment target does not necessarily mean the recruitment strategy is adequate.

A recruitment method may disproportionately reach one part of the intended population while failing to engage others. In studies where particular groups, settings, or clusters are necessary to answer the research question, sample composition is part of feasibility.

The relevant benchmark should follow the design. Researchers should not impose demographic quotas without methodological justification, but neither should they declare recruitment successful when the resulting sample cannot support the comparisons or representation the study explicitly requires.

Test the Recruitment Strategy, Not Just Participant Willingness

Recruitment feasibility depends partly on the strategy used to reach potential participants. Email, telephone calls, clinician referral, social media, community outreach, institutional announcements, in-person recruitment, and other approaches can perform differently across populations and settings.

Preliminary testing can compare how recruitment channels contribute to identification, response, eligibility, consent, and enrollment. It can also reveal practical costs, staffing requirements, and delays.

If the pilot uses unusually intensive researcher involvement that cannot be sustained during the main study, however, its apparent recruitment success may not be scalable. The conditions used to establish feasibility should resemble the conditions available later.

Use Progression Criteria Where They Improve the Decision

For pilot and feasibility studies, researchers may specify recruitment progression criteria before data collection. These provide a basis for interpreting whether observed recruitment supports progression, requires modification, or indicates serious difficulty.

A traffic-light approach is sometimes used. A recruitment result in a green range may support proceeding, an amber range may indicate that modifications are needed, and a red range may indicate that recruitment is unlikely to support the planned study without substantial change.

The thresholds should be justified for the actual project. There is no universal recruitment percentage that makes every study feasible. Sample requirements, recruitment duration, available sites, population size, resources, and possible corrective strategies all matter.

Ask Whether the Pilot Conditions Can Scale

A pilot may recruit successfully because the principal investigator personally contacts every participant, one exceptionally productive site provides most of the sample, or additional staff temporarily support recruitment.

If those conditions cannot exist in the main study, the pilot has tested the wrong recruitment system.

Before extrapolating, compare the pilot and main study in terms of recruitment personnel, sites, population access, recruitment duration, eligibility criteria, incentives where applicable, communication channels, and participant burden.

The closer the conditions are to those intended for the main study, the more informative the feasibility evidence is likely to be.

Recruitment Feasibility Is Not the Same as the Decision to Proceed

A study can demonstrate that recruitment is feasible and still not proceed. Funding may disappear, the intervention may change, another feasibility problem may emerge, or the research question may become less important.

The reverse can also occur. Recruitment may fall below a prespecified target, but investigators may identify a credible modification, such as adding sites or changing a recruitment process, that makes progression reasonable.

Feasibility asks whether recruitment can work. Progression asks what researchers will do given that evidence and the wider context. The two judgments are related but not identical.

How a Recruitment Funnel Reveals the Real Problem

The final enrollment number is useful, but the recruitment funnel explains whether that number is likely to be reproducible and where the process may need modification.

Common Mistakes When Judging Recruitment Feasibility

Build a Recruitment Funnel Before You Build a Recruitment Assumption

Start with the sample and timeline required by the main study. Work backward through the recruitment process to estimate how many eligible people must be approached, screened, or identified to produce that final number.

Recruitment is only one component of overall study feasibility. Even a strong recruitment pathway cannot compensate for unacceptable retention, impractical procedures, or unusable data. It should therefore be considered alongside the other study processes that may need testing before full implementation.

Before Calling Your Recruitment Plan Feasible, Check

Frequently Asked Questions About Recruitment Feasibility

Recruitment Is Feasible Only If the Pathway Can Deliver the Sample You Actually Need

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