, sequential analysis
or sequential hypothesis testing
is statistical analysis
where the sample size
is not fixed in advance. Instead data is evaluated as it is collected, and further sampling is stopped in accordance with a pre-defined stopping rule
as soon as significant results are observed. Thus a conclusion may sometimes be reached at a much earlier stage than would be possible with more classical hypothesis testing
, at consequently lower financial and/or human cost.
Sequential analysis was first developed by Abraham Wald with Jacob Wolfowitz as a tool for more efficient industrial quality control during World War II.
Essentially the same approach was independently developed at the same time by Alan Turing as part of the Banburismus technique used at Bletchley Park, to test hypotheses about whether different messages coded by German Enigma machines should be connected and analysed together. This work remained secret until the early 1980s.
Sequential analysis has also connection to the problem of gambler's ruin studied by among others Huyghens already in 1657.
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