Codeine and acupuncture for dental pain relief
Use this diagram to explain the symmetry between blocks and treatments in randomised block data and to motivate the additive model:
y = (overall mean) + (effect depending on block)
+ (effect depending on
treatment) + error
Click Colour different blocks.
Drag the centre of the diagram to rotate more generally.
Pain relief score were measured for 32 subjects who were each given one of four treatments (combinations of codeine and acupuncture). They were grouped into blocks of four according to an initial assessment of their pain tolerance and the treatments were randomly allocated to the four subjects in each block. (I.e. a randomised block design was used.)