Effect Size Calculator

The Effect Size Calculator allows users to input group statistics and calculates Cohen’s d, Hedges’ g, and provides an interpretation of the effect size.

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Step-by-Step Guide to Using the Effect Size Calculator

This guide will help you understand how to use the Effect Size Calculator. Follow the steps carefully to input your data and compute various statistical measures.

Step 1: Enter Mean Values

  • Group 1 Mean: Enter the mean value for the first group in the Group 1 Mean field. This is a required field and accepts any number.
  • Group 2 Mean: Enter the mean value for the second group in the Group 2 Mean field. This is a required field and accepts any number.

Step 2: Enter Standard Deviations

  • Group 1 Standard Deviation: Enter the standard deviation for the first group in the Group 1 SD field. This is a required field and must be a non-negative number.
  • Group 2 Standard Deviation: Enter the standard deviation for the second group in the Group 2 SD field. This is a required field and must be a non-negative number.

Step 3: Enter Sample Sizes

  • Group 1 Sample Size: Enter the sample size for the first group in the Group 1 N field. This is a required field and must be an integer of at least 2.
  • Group 2 Sample Size: Enter the sample size for the second group in the Group 2 N field. This is a required field and must be an integer of at least 2.

Step 4: Calculate Results

Once all the input fields are correctly filled, the calculator will automatically compute the following results:

  • Cohen’s d: This value measures the effect size and is calculated using the formula: (group1Mean - group2Mean) / sqrt((pow(group1SD, 2) + pow(group2SD, 2)) / 2). The result is formatted to three decimal places.
  • Hedges’ g: Similar to Cohen’s d, but with a correction for small sample sizes, calculated as: cohensD * (1 - (3 / (4 * (group1N + group2N - 2) - 1))). The result is formatted to three decimal places.
  • Pooled Standard Deviation: This computed value represents a combined standard deviation of both groups and is calculated by the formula: sqrt(((group1N - 1) * pow(group1SD, 2) + (group2N - 1) * pow(group2SD, 2)) / (group1N + group2N - 2)). The result is formatted to three decimal places.
  • Effect Size Interpretation: Provides a qualitative interpretation of the effect size using Cohen’s d value: ‘Very Small’ for Cohen’s d < 0.2, 'Small' for 0.2 &leq; Cohen's d < 0.5, 'Medium' for 0.5 &leq; Cohen's d < 0.8, and 'Large' for Cohen's d &geq; 0.8.

Step 5: Review and Interpret Results

After obtaining the results, you can interpret the effect sizes according to the guidelines provided. Use the outcome to understand the magnitude and importance of differences between your two groups.