Effi Effect Size Converter
Prof. Dr. Doğukan ÖZENAnkara University, Faculty of Veterinary Medicine, Department of Biostatistics06070, Ankara, Türkiye

Transparent effect-size conversions

Choose the analysis context first. Effi only performs conversions that have a defensible mathematical relationship and explains when a conversion is approximate, restricted, or not identifiable.

This changes display only, not the calculation.

Required parameters

Enter the analysed group size; no automatic default is used.
Enter the analysed group size; no automatic default is used.
Number of paired subjects or matched pairs.
Total analysed observations, not a planned sample size.
For one-way ANOVA, df₁ = k − 1.
May be derived as N − k when both are entered.
Use this instead of df₁ when df₁ = k − 1.
Required for Cramér’s V.
A 2×2 table is required for φ.
F, χ², V, f, η² and ω² do not contain a sign.

Conversion result

How to use and how to interpret

A statistic is not automatically an effect size. A test statistic also needs its design and degrees of freedom, and some conversions cannot recover direction or the original information.

Step 1 — choose the analysis context

The context controls which statistics are offered and prevents treating a paired measurement or an omnibus ANOVA as an independent two-group comparison.

Step 2 — enter only the parameters that belong to that analysis

Do not use a planned sample size in place of the analysed N. For independent groups, N should equal n₁ + n₂. For ANOVA, df₁ can be obtained from k − 1 and df₂ from N − k only when those values are genuinely applicable.

Important limitations
  • Cohen’s d, Hedges’ g, and t conversions are for two independent groups unless the paired dz option is selected.
  • The OR–d relationship is a logistic-distribution approximation, not an identity.
  • χ² cannot recover a sign; a direction must be supplied if a signed φ, r, or d is requested.
  • A single omnibus F does not identify a unique pairwise d. Effi allows F → d only for df₁ = 1 and marks the direction as user-supplied.
  • Cohen’s f and η²-family measures describe ANOVA-type effects and should not be interpreted as if they were correlations.
Supported relationships
MetricMeaningMain requirements
Cohen’s d / Hedges’ gStandardised mean differencen₁ and n₂ for conversions involving t, r or g
r / ORAssociation measuresr↔d uses n₁ and n₂; OR↔d is approximate
F / η² / partial η² / ω² / fOmnibus or ANOVA-type effectsdf₁ and df₂ for F and ω² pathways; k may supply df₁
χ² / φ / VContingency-table associationN; rows and columns for V; 2×2 for φ

Bulk conversion from CSV

Upload a CSV, select the numeric source-value column, and use the same settings above for every row. Invalid rows are retained with an explanation.