🧠 MindStat

⚠️ Example not found

This example does not exist or may have been moved.

← Browse all examples
📐
Sample Size

Sample Size for a Master's Thesis — Step-by-Step Guide

How to calculate the minimum sample size for a two-group comparison study. Covers Cohen's d, z-values, attrition buffer, and APA-7 a priori power analysis statement.

📊 n = 63/group (N = 126) — recruit 75 with 15% buffer
← All Examples 📄 Full Examples Page ▶ Open in MindStat App
Step-by-step solution
View in context →

📐 20 · Sample Size for a Master's Thesis

How Many Participants Do I Need? — Two-Group Comparison
Sample Size
Research Question: A master's student compares blended vs. traditional teaching (two groups). What is the minimum sample size to detect a medium effect (d = 0.5) with 80% power at α = .05?
ParameterValueWhy
Effect size d0.5Medium — Cohen (1988) convention
α0.05Standard significance level
Power (1−β)0.8080% — minimum recommended
Formula — n per group
$$n = \frac{2(z_{\alpha/2} + z_\beta)^2}{d^2}$$
  1. 1
    Find z-values:
    $$z_{\alpha/2} = z_{0.025} = 1.96 \qquad z_\beta = z_{0.20} = 0.842$$
  2. 2
    Calculate n per group:
    $$n = \frac{2(1.96 + 0.842)^2}{(0.5)^2} = \frac{2 \times 7.857}{0.25} = \frac{15.713}{0.25} \approx 63$$
  3. 3
    Add 15% attrition buffer (recommended):
    $$n_{adj} = \frac{63}{1 - 0.15} = \frac{63}{0.85} \approx 75 \text{ per group}$$
  4. 4
    Total sample to recruit:
    $$N_{total} = 75 \times 2 = 150 \text{ participants}$$
63
Min. per group
75
Recruit per group
150
Total N
80%
Power
APA-7
An a priori power analysis (Cohen, 1988) indicated that 63 participants per group (total N = 126) were required to detect d = 0.50 with 80% power (α = .05, two-tailed). To account for attrition, 75 participants per group (total N = 150) were recruited.

Related Examples