For a binomial distribution with n trials and probability of success p on each trial, the standard deviation (sigma or σ) is defined as: σ = √np(1 - p). The standard deviation is a measure of the amount of variation from the mean, denoted in statistics as "μ" the Greek letter mu.
Continue ReadingAs an example, imagine a coin that is flipped 100 times, with a binomial distribution defined by the number of heads. In this case:
n = 100
p = 0.5
μ = np = 100 x 0.5 = 50
σ = √100 x 0.5(1 - 0.5) = √25 = 5
In other words, out of 100 coin flips, one can expect the number of heads on average to fall between 50 +/- 5, or between 45 and 55.
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