1. What is G*Power Sample Size Calculation?

G*Power is a statistical power analysis program used to compute sample sizes for various statistical tests. It helps researchers determine the minimum number of participants needed to detect an effect of a given size with a specified level of confidence.

2. How Does the Calculator Work?

The calculator uses power analysis principles:

Where:

• \( \alpha \) — Significance level (Type I error probability)
• \( \text{power} \) — Probability of detecting an effect (1 - Type II error)
• \( \text{effect size} \) — Standardized measure of the effect magnitude
• \( n \) — Required sample size per group

Explanation: The calculation considers the trade-off between statistical power, effect size, and significance level to determine the minimum sample size needed.

3. Importance of Sample Size Calculation

Details: Proper sample size calculation ensures studies have adequate power to detect effects while avoiding unnecessary resource expenditure on overly large samples.

4. Using the Calculator

Tips: Enter desired alpha level (typically 0.05), power (typically 0.8), estimated effect size, and select test type. All values must be valid (0 < α < 1, 0 < power < 1, effect size > 0).

5. Frequently Asked Questions (FAQ)

Q1: What is a good power level?
A: 0.8 (80%) is standard, meaning an 80% chance of detecting an effect if it exists. Higher power reduces Type II errors but requires larger samples.

Q2: How do I estimate effect size?
A: Use pilot data, literature review, or conventions (small=0.2, medium=0.5, large=0.8 for Cohen's d).

Q3: What if my sample size is too large?
A: Consider whether the effect size is clinically meaningful. Very large samples may detect trivial effects.

Q4: Does this work for all study designs?
A: The calculator provides basic estimates. Complex designs may require specialized power analysis.

Q5: What about dropout rates?
A: Increase your target sample size to account for expected dropout (e.g., if you expect 20% dropout, divide calculated n by 0.8).