Lady Tasting Tea

Muriel Bristol

In the design of experiments in statistics, the lady tasting tea is a famous randomized experiment devised by English statisticia Ronald A. Fisher and reported in his book ‘The Design of Experiments’ (1935). The experiment is the original exposition of Fisher’s notion of a ‘null hypothesis’ (what you expect to happen before you run an experiment, i.e. nothing). Fisher’s description is less than ten pages in length and is notable for its simplicity and completeness regarding terminology, calculations, and design of the experiment. The example is loosely based on an event from his life. The lady in question was biologist Muriel Bristol.

Bristol claimed to be able to tell whether the tea or the milk was added first to her daily cup of tea. Fisher proposed to give her eight cups, four of each variety, in random order. One could then ask what the probability was for her getting the number she got correct, but just by chance. She got all eight cups correct. In popular science, David Salsburg published a book entitled ‘The Lady Tasting Tea,’ which describes Fisher’s experiment and ideas on randomization.

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