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. 2018 Jan 18:10:153-157.
doi: 10.2147/CLEP.S146397. eCollection 2018.

Guidance for using pilot studies to inform the design of intervention trials with continuous outcomes

Melanie L Bell  1 , Amy L Whitehead  2 , Steven A Julious  2
Affiliations

Guidance for using pilot studies to inform the design of intervention trials with continuous outcomes

Melanie L Bell et al. Clin Epidemiol. .

Abstract

Background: A pilot study can be an important step in the assessment of an intervention by providing information to design the future definitive trial. Pilot studies can be used to estimate the recruitment and retention rates and population variance and to provide preliminary evidence of efficacy potential. However, estimation is poor because pilot studies are small, so sensitivity analyses for the main trial's sample size calculations should be undertaken.

Methods: We demonstrate how to carry out easy-to-perform sensitivity analysis for designing trials based on pilot data using an example. Furthermore, we introduce rules of thumb for the size of the pilot study so that the overall sample size, for both pilot and main trials, is minimized.

Results: The example illustrates how sample size estimates for the main trial can alter dramatically by plausibly varying assumptions. Required sample size for 90% power varied from 392 to 692 depending on assumptions. Some scenarios were not feasible based on the pilot study recruitment and retention rates.

Conclusion: Pilot studies can be used to help design the main trial, but caution should be exercised. We recommend the use of sensitivity analyses to assess the robustness of the design assumptions for a main trial.

Keywords: feasibility; pilot; power; randomized controlled trial; sample size; sensitivity analysis.

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Conflict of interest statement

Disclosure Professor MLB is supported by the University of Arizona Cancer Center, through NCI grant P30CA023074. Professor SAJ is funded by the University of Sheffield. Dr ALW was funded by a University of Sheffield studentship. The authors report no other conflicts of interest in this work.

Figures

Figure 1
Figure 1
Mean difference in FACT-G scores between pilot study intervention and control arms with confidence intervals. Abbreviations: FACT-G, Functional Assessment of Cancer Therapy-Genera; MID, minimum important difference.
See this image and copyright information in PMC

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