Pilot Study Sample Size Calculator

This pilot sample size calculation helps researchers determine the minimum number of participants needed for a pilot study. It uses a confidence interval approach in which the researcher sets an estimate of the minimum acceptable completion rate required for a larger, definitive trial to be feasible (e.g. to do a definitive trial, a 70% minimum response rate is required). The sample size is then calculated so that the lower limit of the confidence interval, with its width determined by the margin of error (typically 0.10), meets or exceeds this minimum rate. This ensures the pilot study provides reliable data to determine whether to proceed with a full-scale trial while also accounting for potential patient dropouts.

Calculations derived from Thabane, L., Ma, J., Chu, R., Cheng, J., Ismaila, A., Rios, L. P., Robson, R., Thabane, M., Giangregorio, L., & Goldsmith, C. H. (2010). A tutorial on pilot studies: the what, why and how. BMC Medical Research Methodology, 10(1), 1.

Sample Size for Pilot Studies

\( n = \frac{z^2 \cdot p \cdot (1 - p)}{E^2} \)
\( \text{Adjusted Sample Size} = \left\lceil \frac{n}{1 - (\text{dp} / 100)} \right\rceil \)

Understanding Input Variables

  • \( z \): The z-score corresponding to the desired confidence level (e.g., 1.96 for 95% confidence).
  • \( p \): The estimated proportion of the outcome in the population (e.g., 0.5 for maximum variability).
  • \( E \): The margin of error (e.g., 0.05 for ±5%).
  • \( n \): The minimum sample size required for the pilot study, rounded up to the nearest integer using the ceiling function (\( \lceil \cdot \rceil \)).
  • \( \text{dp} \): The expected dropout percentage (e.g., 10%).
  • \( \text{Adjusted Sample Size} \): The final sample size, adjusted for expected dropouts, rounded up to the nearest integer using the ceiling function (\( \lceil \cdot \rceil \)).

Why Use the Pilot Study Sample Size Calculator?

Conducting a pilot study is a critical step in ensuring the success of a larger clinical trial. However, determining the appropriate sample size for a pilot study can be challenging. This calculator simplifies the process by providing a quick and accurate estimate of the minimum number of participants needed for your pilot study.

Key Benefits:

  • Save Time and Resources: By accurately estimating the sample size, you can avoid over- or under-recruiting participants, saving both time and resources.
  • Improve Study Design: A well-designed pilot study can help identify potential issues in your main trial, such as recruitment challenges or data collection problems.
  • Enhance Feasibility: Pilot studies are essential for assessing the feasibility of a larger trial. This calculator ensures that your pilot study is adequately powered to provide meaningful insights.
  • Boost Confidence: Knowing that your pilot study is based on a statistically sound sample size can increase your confidence in the results and the subsequent main trial.

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