Incomplete block designs for the minimisation of order and carry-over effects in sensory analysis

Two important considerations for experimental designs for sensory evaluation are order and carry-over effects. Ideally each sample would be presented equally often in each order and would be preceded equally often by every other sample. Williams (1949) gives a number of designs which achieve this but only for complete block designs. We describe methods for generating incomplete block designs which are approximately, balanced for carry-oner effects. Using the cyclic structure of cyclic designs as in Davis and Hall (1969), we obtain designs balanced for order effects and nearly balanced for carry-over effects. We describe a computer intensive discrete optimisation method which can be used when a cyclic design is not possible. (C) 1997 Elsevier Science Ltd.