#randomization

Design robust RCT with appropriate statistical power. Study design: 1. Define primary outcome clearly (e.g., change in depression score). 2. Choose randomization method (simple, block, stratified). 3. Blinding strategy (single, double, triple-blind where possible). 4. Control group selection (placebo, wait-list, treatment-as-usual). Power analysis using G*Power: 1. Set α = 0.05, power = 0.80. 2. Estimate effect size from pilot data or literature (Cohen's d). 3. Calculate minimum sample size, add 20% for dropouts. Example: t-test, medium effect (d=0.5), requires n=64 per group, with dropout n=80 per group. Randomization tools: Research Randomizer, RedCap. Registration: ClinicalTrials.gov before recruitment. Monitor for interim analyses and stopping rules.

Maximize internal validity through experimental control. Threats to internal validity (Campbell & Stanley): 1. History: external events during study. Control: randomization, brief study duration. 2. Maturation: natural changes over time. Control: control group, random assignment. 3. Testing: effects of pretesting. Control: Solomon four-group design, posttest-only design. 4. Instrumentation: changes in measurement. Control: standardized protocols, calibration. 5. Regression to mean: extreme scores regress toward average. Control: random assignment, cutoff-based assignment analysis. 6. Selection: systematic differences between groups. Control: randomization, matching. 7. Mortality: differential dropout. Control: intent-to-treat analysis, retention strategies. Design features: random assignment is gold standard. Manipulation checks ensure independent variable was successfully manipulated. Attention controls eliminate placebo effects.