Examples
Worked examples
- Is an instance
A team planning a national multi-site trial of a new smoking-cessation program first runs a pilot at two sites, enrolling 40 participants through the exact intended recruitment and randomization procedures, to estimate the achievable recruitment rate, refine the intervention delivery manual, and confirm the primary outcome measure captures what it is meant to before committing funding to the full-scale trial.
- Is an instance
Before fielding a new patient-reported outcome questionnaire in a definitive study, researchers pilot it with 25 patients to test comprehension, completion time, and item non-response rates, revising confusing items based on what the pilot shows before the instrument is locked into the main study protocol.
Counter-examples
Looks similar, but isn't
- Not an instance
A Phase I first-in-human dose-escalation trial testing the safety and tolerability of a novel drug in 20 healthy volunteers is not a pilot study in the research-methodology sense, despite its small sample size — its purpose is establishing a maximum tolerated dose and safety profile for the drug itself, a defined stage in the regulatory drug-development pathway, not testing the feasibility of a future study’s methods.
- Not an instance
A feasibility assessment that surveys clinicians’ willingness to refer patients and reviews historical enrollment records, without administering any part of the actual planned intervention or protocol to any participant, is a feasibility study but not a pilot study — a pilot specifically requires running a scaled-down version of the intended protocol itself, not just assessing feasibility through indirect means.
Editorial commentary
What makes a study a “pilot”
A pilot study runs a scaled-down version of the actual protocol planned for a future, full-scale study — the same recruitment approach, the same intervention delivery, the same outcome measures, the same data-collection procedures — on a much smaller sample. That’s the operational boundary: a study only counts as a pilot if it is testing the intended methods of a specific future study, not just gathering general background information about whether a topic is worth studying. The classic framing, from the conceptual-framework paper behind the CONSORT pilot-trial extension, is that a feasibility study “asks whether something can be done, should we proceed with it, and if so, how,” while a pilot study is “a study in which a future study, or part of a future study, is conducted on a smaller scale” — and, crucially, “all pilot studies are feasibility studies but not all feasibility studies are pilot studies” (Eldridge et al., PLOS ONE, 2016). A pilot is one specific way of answering a feasibility question: by actually running a miniature version of the real thing.
Pilot study vs. feasibility study
Feasibility is the broader umbrella. A feasibility study can address whether a study “can be done” through methods that never touch the intervention at all — a survey of clinician willingness to refer patients, a review of how many eligible patients exist in a given health system, an audit of whether the planned data-collection forms are logistically workable. A pilot study is the specific subtype of feasibility study that does this by running an actual scaled-down trial or study. Every pilot is a feasibility exercise; not every feasibility exercise is a pilot. On this site’s clinical trial feasibility assessment guide, most of what sponsors evaluate before committing to a protocol (site capability, projected enrollment, budget) sits in that broader feasibility category — a pilot study is the narrower, hands-on subset of that work.
Pilot study vs. Phase I clinical trial
“Pilot” is sometimes used loosely to describe a small early-phase drug trial, but a Phase I trial is a distinct regulatory concept, not a synonym. A Phase I trial exists to establish a drug or biologic’s safety, tolerability, and dosing (often via dose-escalation in a small group of participants) as a defined stage in the regulatory drug-development pathway. A pilot study, by contrast, is a methodological device used at any stage or in any field — behavioral research, health services research, education, social science — to test whether the machinery of a planned future study will actually work. A small, early trial can be both a Phase I trial and, incidentally, feasibility-generating for later trial logistics, but the two labels answer different questions and shouldn’t be used interchangeably.
What a pilot study is used to establish
Typical objectives of a pilot study include:
- Recruitment and retention rates — how many eligible participants can realistically be enrolled and followed up per unit time, used to sanity-check the recruitment assumptions in a full-scale study protocol.
- Acceptability and adherence — whether participants will actually tolerate and complete the intervention or data-collection burden as designed.
- Instrument and outcome-measure performance — whether a questionnaire, assay, or outcome definition works as intended (comprehension, completion time, missing-data patterns) before it’s locked into a definitive study.
- Preliminary parameter estimates — a rough effect size or outcome variance that can inform (not replace) a formal power/sample-size calculation for the full-scale study. Methodologists caution against treating a pilot’s effect estimate as precise: with a small sample the confidence interval around it is typically wide, so it should be used conservatively rather than plugged directly into a sample-size formula as if it were a definitive estimate.
- Operational and logistical issues — problems with randomization procedures, data capture, staffing, or protocol adherence that are far cheaper to fix before a full-scale rollout than during one.
What a pilot study is not designed to do is formally test whether the intervention works. Pilot studies are typically underpowered for a definitive effectiveness comparison, and treating a promising pilot result as evidence of efficacy is a well-documented misuse of the design.
Internal vs. external pilots
An external pilot is a standalone study, run and reported separately, whose participants are not included in the later full-scale study’s analysis. An internal pilot is the initial portion of the full-scale study itself — run under the same protocol and, if it meets pre-specified feasibility criteria, continued seamlessly into the definitive study, with its participants’ data carried forward into the final analysis. Which design is appropriate, and how continuation criteria (sometimes called “progression criteria” — explicit, pre-specified thresholds for recruitment rate, adherence, or data completeness that determine whether the full-scale study proceeds, proceeds with modifications, or is abandoned) are set, is itself part of what a pilot study’s design has to specify up front.
Reporting a pilot study
The CONSORT extension for randomised pilot and feasibility trials (Eldridge et al., 2016) sets reporting expectations distinct from a standard RCT report: results should be presented descriptively, with confidence intervals around feasibility outcomes (recruitment rate, retention, adherence), rather than as formal hypothesis tests of clinical effectiveness with p-values implying a definitive result. A pilot study’s protocol and progression criteria should ideally be specified in advance, the same way a full-scale trial’s would be, so that “the pilot succeeded” isn’t determined after the fact by whichever result happened to occur.
Where pilot studies fit in study design more broadly
Pilot studies sit early in the sequence covered by this site’s broader overview of clinical study design types and the more detailed walkthrough of designing a clinical trial (endpoints, sample size, randomization, and the statistical analysis plan) — a pilot’s findings are typically an input into finalizing those elements, not a substitute for them.
Machine-readable encodings
Use in your systems
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