Читать книгу Medical Statistics - David Machin - Страница 116

Data that can take only a 0 or 1 response, such as treatment failure or treatment success, follow the Binomial distribution provided the underlying population response rate π does not change. The Binomial probabilities are calculated from

(4.1)

for successive values of r from 0 through to n. In the above n! is read as n factorial and r! as r factorial. For r = 4, r! = 4 × 3 × 2 × 1 = 24. Both 0! and 1! are taken as equal to unity. It should be noted that the expected value for r, the number of successes yet to be observed if we treated n patients, is nπ. The potential variation about this expectation is expressed by the corresponding standard deviation .