TY - JOUR
T1 - Sample size determination for mediation analysis of longitudinal data
AU - Pan, Haitao
AU - Liu, Suyu
AU - Miao, Danmin
AU - Yuan, Ying
N1 - Funding Information:
Yuan’s research was partially supported by grants CA154591, CA016672, and 5P50CA098258 from the National Cancer Institute. Miao’s research was partially supported by Military Health Care Key Projects during the Twelfth Five-year Plan Period. The above funds supported the authors to conduct statistical analysis, program code for producing results and write the manuscript and interpret the results.
Publisher Copyright:
© 2018 The Author(s).
PY - 2018/3/27
Y1 - 2018/3/27
N2 - Background: Sample size planning for longitudinal data is crucial when designing mediation studies because sufficient statistical power is not only required in grant applications and peer-reviewed publications, but is essential to reliable research results. However, sample size determination is not straightforward for mediation analysis of longitudinal design. Methods: To facilitate planning the sample size for longitudinal mediation studies with a multilevel mediation model, this article provides the sample size required to achieve 80% power by simulations under various sizes of the mediation effect, within-subject correlations and numbers of repeated measures. The sample size calculation is based on three commonly used mediation tests: Sobel's method, distribution of product method and the bootstrap method. Results: Among the three methods of testing the mediation effects, Sobel's method required the largest sample size to achieve 80% power. Bootstrapping and the distribution of the product method performed similarly and were more powerful than Sobel's method, as reflected by the relatively smaller sample sizes. For all three methods, the sample size required to achieve 80% power depended on the value of the ICC (i.e., within-subject correlation). A larger value of ICC typically required a larger sample size to achieve 80% power. Simulation results also illustrated the advantage of the longitudinal study design. The sample size tables for most encountered scenarios in practice have also been published for convenient use. Conclusions: Extensive simulations study showed that the distribution of the product method and bootstrapping method have superior performance to the Sobel's method, but the product method was recommended to use in practice in terms of less computation time load compared to the bootstrapping method. A R package has been developed for the product method of sample size determination in mediation longitudinal study design.
AB - Background: Sample size planning for longitudinal data is crucial when designing mediation studies because sufficient statistical power is not only required in grant applications and peer-reviewed publications, but is essential to reliable research results. However, sample size determination is not straightforward for mediation analysis of longitudinal design. Methods: To facilitate planning the sample size for longitudinal mediation studies with a multilevel mediation model, this article provides the sample size required to achieve 80% power by simulations under various sizes of the mediation effect, within-subject correlations and numbers of repeated measures. The sample size calculation is based on three commonly used mediation tests: Sobel's method, distribution of product method and the bootstrap method. Results: Among the three methods of testing the mediation effects, Sobel's method required the largest sample size to achieve 80% power. Bootstrapping and the distribution of the product method performed similarly and were more powerful than Sobel's method, as reflected by the relatively smaller sample sizes. For all three methods, the sample size required to achieve 80% power depended on the value of the ICC (i.e., within-subject correlation). A larger value of ICC typically required a larger sample size to achieve 80% power. Simulation results also illustrated the advantage of the longitudinal study design. The sample size tables for most encountered scenarios in practice have also been published for convenient use. Conclusions: Extensive simulations study showed that the distribution of the product method and bootstrapping method have superior performance to the Sobel's method, but the product method was recommended to use in practice in terms of less computation time load compared to the bootstrapping method. A R package has been developed for the product method of sample size determination in mediation longitudinal study design.
KW - Longitudinal study
KW - Mediation analysis
KW - Sample size determination
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U2 - 10.1186/s12874-018-0473-2
DO - 10.1186/s12874-018-0473-2
M3 - Article
C2 - 29580203
AN - SCOPUS:85045183490
SN - 1471-2288
VL - 18
JO - BMC Medical Research Methodology
JF - BMC Medical Research Methodology
IS - 1
M1 - 32
ER -