The titration of vaccinia virus by the pock counting technique

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Abstract
Ninety-seven groups of five-membrane pock counts from 115 titrations of vaccinia virus preparations were examined in an attempt to identify the statistical distribution followed by such counts, and to obtain an estimate of the overall coefficient of variation of the technique. It was found that the distribution of counts was neither Poissonian nor normal, and that the count variances ‘wandered’ so extensively that no valid estimate of the overall coefficient of variation was possible. Nor was it possible to assess the intrinsic reproducibility of the test, although it is empirically a useful one.