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TRUST Research Center
🐭 Animal Research Tool

The Resource Equation Approach

Calculate minimum and maximum sample sizes for animal studies using the resource equation method. Based on Arifin & Zahiruddin (2017).

📊

Between Groups

One-way ANOVA or independent t-test design

Min per Group
—
animals
Max per Group
—
animals
Min Total
—
animals
Max Total
—
animals
Formulas Used
Min n/group = ROUNDUP(10/k + 1, 0)
Max n/group = ROUNDDOWN(20/k + 1, 0)
Min Total = Min n × k   |   Max Total = Max n × k
// Error DF = N − k = k(n−1), target range: 10–20
💡 How it works The resource equation keeps the error degrees of freedom (DF) between 10 and 20. For a one-way ANOVA with k groups, DF = k(n−1). Solving for n gives the formulas above.
🔄

Repeated Measures

One within-factor repeated-measures ANOVA

Min Animals
—
total
Max Animals
—
total
Formulas Used
Min N = ROUNDUP(10/(r−1) + 1, 0)
Max N = ROUNDDOWN(20/(r−1) + 1, 0)
// Error DF = (N−1)(r−1), target range: 10–20
💡 How it works For repeated-measures designs with one group, the within-subject error DF = (N−1)(r−1). Only one group is involved, so n = N. If animals are sacrificed at each measurement, multiply by r.
🔀

Between Groups + Repeated Measures

One between and one within factor repeated-measures ANOVA

Min per Group
—
animals
Max per Group
—
animals
Min Total
—
animals
Max Total
—
animals
Formulas Used
Min n/group = ROUNDUP(10/(k×r) + 1, 0)
Max n/group = ROUNDDOWN(20/(k×r) + 1, 0)
Min Total = Min n × k   |   Max Total = Max n × k
// Error DF = k×r×(n−1), target range: 10–20
💡 How it works For mixed designs, total error DF = k×r×(n−1), combining between-subject and within-subject error. Solving for n gives the per-group formulas. If animals are sacrificed at each measurement, multiply by r.
Reference
Arifin, W. N., & Zahiruddin, W. M. (2017). Sample size calculation in animal studies using resource equation approach. Malaysian Journal of Medical Sciences, 24(5), 101–105. DOI: 10.21315/mjms2017.24.5.11