# In terms of the parameters of the probability mass function, what is the formula for the standard deviation of a Poisson distribution?

f (x ) = ${e}^{-} m$ ${m}^{x}$ / x !, x = 0, 1, 2 ... $\infty$ is the p.d.f. of Poisson distribution. Its variance is 'm' , the parameter in the p.d.f. and hence S.D = sqrtm.