Pilot and feasibility trials

Pilot and Feasibility Trials

Pilot and feasibility trials are small-scale studies conducted before a full-scale randomized controlled trial (RCT). Their primary purpose is not to assess efficacy but to evaluate whether a larger trial is feasible and how it should be designed. These preliminary studies are essential for identifying potential issues related to recruitment, intervention delivery, data collection, and participant engagement. By refining the trial protocol and logistics, they increase the likelihood of success in the main trial.

Defining the Purpose

The distinction between feasibility and pilot trials is important. A feasibility trial explores whether a larger trial can be done and examines elements such as recruitment processes, participant retention, and adherence to the intervention. A pilot trial is a scaled-down version of the planned full trial, often used to test procedures, logistics, and trial flow. For example, a feasibility objective might ask: "Can 80% of eligible patients be recruited within six months?" or "Are participants willing to adhere to the intervention for 12 weeks?"

Setting Clear Objectives

Well-defined objectives are critical to guide the design and evaluation of a pilot or feasibility trial. Common objectives include estimating recruitment and retention rates, assessing intervention fidelity and adherence, evaluating randomization procedures, and measuring the completeness and quality of data collection. Researchers may also examine the acceptability of the intervention and study procedures from the perspective of participants. For instance, objectives may include achieving a recruitment rate of 10 participants per month or ensuring 90% follow-up data completion.

Choosing the Study Design

The design of a pilot or feasibility trial should resemble the intended full-scale trial but be scaled down in terms of size and duration. Common formats include parallel group RCTs, cluster RCTs, or single-arm studies. The emphasis is on process evaluation and descriptive results rather than hypothesis testing. Statistical significance is not typically the goal; instead, the focus is on collecting useful information to guide the future trial.

Defining Key Outcomes

Feasibility outcomes are the core of these studies. These may include recruitment and retention rates, adherence to the intervention, protocol deviations, and data completeness. Although pilot trials may also collect clinical outcomes, these are generally used to estimate variability or inform future sample size calculations rather than to draw definitive conclusions. Participant acceptability and safety should also be assessed through feedback, monitoring of adverse events, and qualitative interviews when appropriate.

Sample Size Considerations

Unlike full-scale trials, pilot and feasibility studies are not powered to detect treatment effects. Instead, their sample size should be sufficient to assess feasibility objectives. A typical range is 12–30 participants per group, depending on the goals of the study. A common rule of thumb is to enroll 10–15 participants per group when assessing recruitment rates, adherence, or data collection procedures.

Planning the Intervention and Procedures

One major goal of a pilot trial is to test the intervention and logistical procedures. This includes evaluating the delivery method, timing, dose, and fidelity of the intervention. Researchers should also test recruitment strategies, data collection instruments, randomization procedures, and participant follow-up schedules. For example, different recruitment approaches (e.g., social media vs. clinic-based) may be tested to determine

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Bibliography

1. Eldridge SM, Chan CL, Campbell MJ, et al. CONSORT 2010 statement: extension to randomised pilot and feasibility trials. BMJ. 2016;355:i5239.
2. Thabane L, Ma J, Chu R, et al. A tutorial on pilot studies: the what, why and how. BMC Medical Research Methodology. 2010;10:1.
3. Arain M, Campbell MJ, Cooper CL, Lancaster GA. What is a pilot or feasibility study? A review of current practice and editorial policy. BMC Medical Research Methodology. 2010;10:67.
4. Lancaster GA, Dodd S, Williamson PR. Design and analysis of pilot studies: recommendations for good practice. Journal of Evaluation in Clinical Practice. 2004;10(2):307–312.
5. Billingham SA, Whitehead AL, Julious SA. An audit of sample sizes for pilot and feasibility trials is necessary. BMJ Open. 2013;3(4):e002298.

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Adapted for educational use. Please cite relevant trial methodology sources when using this material in research or teaching.