2-Arm Sample Size Calculator
Here's a comprehensive table summarizing the key aspects of 2-Arm Sample Size calculation:
| Aspect | Details |
|---|---|
| Definition | A method to determine the number of participants needed in two intervention groups for a study. |
| Calculation Methods | Parametric, non-parametric, and simulation methods are used. |
| Key Factors | Effect size, significance level (α), power (1-β), dropout rates, variability. |
| Common Formula (Binary Outcome) | n = [(Z_α/2 + Z_β)^2 * (p1(1-p1) + p2(1-p2))] / (p1 - p2)^2. |
| Common Formula (Continuous Outcome) | n = 2(Z_1-α/2 + Z_1-β)^2 * σ^2 / δ^2, where σ is population SD and δ is target mean difference2. |
| Effect on Sample Size | Halving the target difference quadruples the sample size for a two-arm, 1:1 parallel group superiority trial with a continuous outcome5. |
| Time-to-Event Studies | Traditional methods assume proportional hazards (PH) or exponentially distributed survival times. Newer methods allow for non-PH scenarios1. |
| Exact Tests | Can be used for smaller sample sizes in phase II trials, allowing trade-offs between α, power, and sample size3. |
| Compliance Considerations | Non-compliance can increase required sample size. For example, a study showed an increase from 2480 to 2616 subjects per arm when accounting for non-compliance4. |
| Sensitivity Analysis | Prudent to assess potential effects of misspecification of key assumptions (e.g., control response rate for binary outcomes or anticipated variance for continuous outcomes)5. |
| Applications | Used in clinical trials, A/B testing, and comparative studies. |
This table provides a concise overview of the essential elements in 2-Arm Sample Size calculation, including definitions, methods, key factors, common formulas, and considerations for different types of studies. It's important to note that sample size calculation is a critical step in study design, as it directly impacts the study's ability to detect meaningful differences between groups and the overall feasibility of the research.