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The standard deviation of a binomial distribution is ............

  • A.\(np\)
  • B.\(npq\)
  • C.\(\sqrt{npq}\)
  • D.\(np^{2}q^{2}\)

Answer: C

The standard deviation of a binomial distribution is \(\sqrt{npq}\).

For a binomial distribution with n trials, probability of success p and probability of failure q = 1 - p, the mean and variance are:

\[ \begin{aligned} \mu &= np \\ \sigma^{2} &= npq \\ \sigma &= \sqrt{npq} \end{aligned} \]

So np is the mean, not the standard deviation, and npq is the variance; the standard deviation is its square root. The expression \(np^{2}q^{2}\) has no role in the binomial distribution. For example, with n = 100 and p = q = 0.5, the mean is 50, the variance 25 and the standard deviation 5.

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