Module 4 · Lesson 15 of 22
One-way and two-way ANOVA
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Learning objectives
- Distinguish one-way from two-way ANOVA.
- Interpret F, main effects and interaction.
- Follow up with planned comparisons.
What ANOVA does
One-way ANOVA compares means across one categorical factor. Two-way ANOVA adds a second factor and estimates their interaction.
A significant interaction means main-effect interpretation must be qualified — the effect of one factor depends on the level of the other.
Garment-factory example
Compare seam strength across four thread types; then analyse thread type and SPI together to see whether the thread effect changes with SPI.
Method
- Define response and factors.
- Randomise where possible.
- Fit model in a free tool; inspect residuals.
- Interpret interaction before main effects.
Common mistakes
- Running many pairwise t-tests instead of ANOVA.
- Interpreting main effects when a strong interaction exists.
Knowledge check
Pick one answer per question. Explanations appear after you submit.
1. A significant ANOVA F says:
2. Strong interaction means:
Author: NOSK.life · Last reviewed: 2026-07-21