zzpower: Power Analysis Calculator for Two-Group Parallel Designs

The zzpower package provides an interactive 'Shiny' application for power analysis and sample size calculations specifically designed for two-group parallel clinical trial designs. The application supports multiple effect size specifications, accounts for dropout rates and unequal group allocation ratios, and provides interactive visualizations with downloadable reports.

Details

A comprehensive 'Shiny' application for conducting power analysis and sample size calculations for two-group parallel clinical trial designs.

Key Features

Multiple Effect Size Methods: Supports Cohen's d, percentage reductions, difference in change scores, and treatment group changes
Comprehensive Design Considerations: Accounts for dropout rates, drop-in rates, and unequal group allocation ratios
Interactive Visualizations: Real-time power curves and detailed results tables
Report Generation: Downloadable reports in PDF, HTML, or Word formats
Advanced Settings: Configurable Type I error rates and one-sided vs two-sided testing

Getting Started

To launch the interactive application, simply run:


library(zzpower)
launch_zzpower()

Effect Size Methods

The application supports four different approaches to specifying effect sizes:

Standard Deviation Units (Cohen's d):: Direct specification of standardized effect sizes
Percent Reduction:: Effect size specified as percentage reduction from placebo
Difference in Change Scores:: Absolute difference between treatment groups in outcome units
Change in Active Group:: Specifying the treatment group change directly

Sample Size Calculations

The application calculates both intention-to-treat (ITT) and completer sample sizes, accounting for:

Expected dropout rates
Drop-in rates (control group receiving treatment)
Unequal randomization ratios between groups

References

Cohen, J. (1988). Statistical Power Analysis for the Behavioral Sciences (2nd ed.). Lawrence Erlbaum Associates.

Author

Ronald "Ryy" G. Thomas