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Required sample size to detect mediation in 3-level implementation studies.

Nathaniel J Williams1,2, Kristopher J Preacher3, Paul D Allison4

  • 1Institute for the Study of Behavioral Health and Addiction, Boise State University, 1910 University Drive, Boise, ID, 83725-1940, USA. natewilliams@boisestate.edu.

Implementation Science : IS
|October 1, 2022
PubMed
Summary
This summary is machine-generated.

Many implementation science studies lack statistical power for 3-level mediation analysis. Achieving adequate power requires large effect sizes and at least 40 highest-level units for robust mediation detection.

Keywords:
Indirect effectsMediationMplusMultilevelStatistical power

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Area of Science:

  • Implementation Science
  • Statistical Methods
  • Multilevel Modeling

Background:

  • Statistical mediation tests are crucial for advancing implementation science.
  • Limited research exists on sample size requirements for 3-level mediation designs common in implementation studies.

Purpose of the Study:

  • To examine the sample sizes needed to detect mediation in 3-level designs.
  • To assess statistical power under various plausible conditions for implementation research.

Main Methods:

  • A Monte Carlo simulation method was used to estimate statistical power.
  • 17,496 3-level mediation designs were analyzed with varying sample sizes, intraclass correlations, and effect sizes.
  • Two statistical models (MVM and MSEM) were used for both 1- and 2-sided hypothesis tests.

Main Results:

  • Adequate statistical power (≥0.8) was achieved in only 1.3%–4.6% of designs.
  • Minimum sample sizes for adequate power were 900 observations (2-sided) or 600 (1-sided).
  • At least one large effect size was necessary for sufficient power across all conditions.

Conclusions:

  • Many 3-level mediation designs in implementation research lack sufficient statistical power.
  • Achieving adequate power necessitates large effect sizes and at least 40 highest-level units.
  • Strategies to enhance power and feasibility of mediation tests in multilevel designs are suggested.