Introduction to pilot and feasibility studies

There are an increasing number of published studies referred to as pilot and feasibility studies. However, there are sometimes differences of opinion as to what these terms mean.

What are pilot and feasibility studies?

A well cited framework suggests the following definitions:

  • A feasibility study asks whether something can be done, should we proceed with it, and if so, how.

  • A pilot study asks the same question but has a specific design feature: in a pilot study a future study, or part of a future study, is conducted on a smaller scale.

The corollary of these definitions is that all pilot studies are feasibility studies but not all feasibility studies are pilot studies. This framework is based on extensive research into the use and opinion of these terms by the research community and more general definitions of the terms:

The framework figure is shown below:

Internal/external pilot studies

Avery et al define internal and external pilot studies as follows:

  • An external pilot is a rehearsal of the main study where the outcome data are not included as part of the main trial outcome data set.

  • In an internal pilot, the pilot phase forms the first part of the trial and the outcome data generated contribute to the final analysis (unless major changes to the protocol are needed).

The choice of design (internal vs. external) should be pre-specified to avoid bias that may result from a decision to include/exclude data from the pilot phase made after pilot data are available. External pilot studies allow for greater flexibility to change the trial design for the main study once the pilot is complete, whereas internal pilot studies may be more efficient if investigators only want to look at the feasibility of aspects such as recruitment that will not change trial design. For more information on this efficiency, see the following paper:

Definitions of pilot and feasibility studies by funders

The definitions in the framework above have been adopted by the UK National Institute for Health and Care Research and the Health Research Board in Ireland to guide researchers applying for funding. The latest update of the UK Medical Research Council (MRC) guidance references these definitions too. We recommend the definitions from the framework because of their simplicity and grounding in robust research.

Incorrect use of the terms pilot and feasibility

Some reviews, as listed below, have highlighted that sometimes a small underpowered effectiveness study is labelled as a pilot or feasibility study. There is therefore a need to raise awareness of the difference between a pilot study that is designed to clarify areas of uncertainty, and a small underpowered study labelled as a pilot that does not comply with definitions and is not reported according to the CONSORT guidance:

Examples of pilot and feasibility studies

Below are some examples of well-conducted and well-reported pilot and feasibility studies:

Why do a pilot or feasibility study?

The purpose of performing pilot and feasibility studies is to give your research the best chance of success. When developing an intervention, the U.K. Medical Research Council (MRC) suggest that a series of pilot or feasibility studies may be needed to target each of the key uncertainties in the design, before moving on to a definitive evaluation.

A pilot or feasibility study in advance of a future definitive study is helpful to investigate areas of uncertainty about the later definitive study, for example, checking participants can be recruited and retained, testing the study protocol, estimating parameters for a sample size calculation for the future definitive study, and exploring potential outcome measures. Assessing feasibility in this way ensures that fewer problems are likely to be encountered in the definitive study. This encourages methodological rigour and higher quality definitive studies.

From a practical point of view, funders often require pilot or feasibility studies to determine whether a definitive study is likely to succeed and hence be worth funding. Moreover, funders often expect applicants to use data from the pilot or feasibility study to plan study duration, number of sites etc.

For further reading on why to do a pilot or feasibility study:

Book chapters on pilot and feasibility studies

  • Ukoumunne, OC, Eddy S, Warren FC. How to use feasibility studies to derive parameter estimates in order to power a full trial. In Complex Interventions in Health: An Overview of Research Methods. Richards, DA, Hallberg, IR. (eds) 2nd. London: Routledge. 2025 (In press)

  • Giangregorio L, Lancaster GA, Thabane L. Chapter 13 Overview of feasibility studies including pilot studies. In Complex Interventions in Health: An Overview of Research Methods. Richards DA, Hallberg IR, Meyer G, Köpke S, Woodford J, Wengström Y, Estabrooks C, Wallin L. (eds.) 2nd edition. London: Routledge. 2025 (In press)

  • Li G, Bai X, Lancaster GA, Thabane L. Users’ guide to the surgical literature: How to assess a pilot trial in surgery. In Evidence-based surgery: understanding and interpreting the surgical literature. Thoma A, Sprague S, Voineskos SH, Serrano PE, Goldsmith CH. (eds.) 2nd edition. Heidelberg: Springer, 2025.

  • Eldridge S, Kerry S. Pilot and Feasibility Studies. In Eldridge S, Kerry S. A Practical Guide to Cluster Randomised Trials in Health Services Research. Chichester: John Wiley; 2012