Randomised Block Design
A randomised block design divides units into blocks based on variables expected to affect the response, then randomly assigns each treatment to units within each block. This design reduces error by controlling for known sources of variation while preserving randomisation.
Real World
Unilever testing three shampoo formulations blocks volunteers by hair type (straight, wavy, curly), then randomly assigns one formulation per person within each block to ensure fair comparison.
Exam Focus
Emphasise that every treatment appears exactly once in each block and that randomisation occurs within, not between, blocks.
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