1. What is Cohen's d Effect Size?

Cohen's d is a measure of effect size that indicates the standardized difference between two means. It's widely used in statistical analysis to quantify the magnitude of differences between groups.

2. How Does the Calculator Work?

The calculator uses Cohen's d formula:

Where:

• \( \text{Mean}_1 \) — Mean of first group
• \( \text{Mean}_2 \) — Mean of second group
• \( \text{Pooled SD} \) — Combined standard deviation of both groups

Explanation: The formula calculates how many standard deviations apart the two means are, providing a standardized measure of effect size.

3. Interpretation of Effect Size

Guidelines:

• Small effect: d ≈ 0.2
• Medium effect: d ≈ 0.5
• Large effect: d ≈ 0.8

These values indicate the practical significance of the difference between groups.

4. Using the Calculator

Tips: Enter the means for both groups and the pooled standard deviation. All values must use the same measurement units.

5. Frequently Asked Questions (FAQ)

Q1: When should I use Cohen's d?
A: Use it when comparing two group means to understand the practical significance of their difference.

Q2: How is pooled standard deviation calculated?
A: Pooled SD combines the standard deviations of both groups, weighted by their sample sizes.

Q3: What's the difference between Cohen's d and t-test?
A: t-test assesses statistical significance (p-value), while Cohen's d measures effect size (magnitude).

Q4: Can Cohen's d be negative?
A: Yes, the sign indicates direction (which mean is larger) but doesn't affect effect size interpretation.

Q5: What are alternatives to Cohen's d?
A: Other effect size measures include Pearson's r, odds ratio, or eta squared, depending on the analysis.