1. Introduction
The Poisson probability distribution is believed to be one of the three most important distributions,
the other two being the binomial and the normal distribution. The mean, μ, and variance,
2, are usually the main features of a given distribution. The mean is a measure of central tendency,
while the variance is a measure of the dispersion, spread or variability of a distribution. If
X is binomial with parameters n, a positive integer, and p, 0 < p < 1, denoted by b(n, p), then
μ = np and 2 = np(1 − p); clearly, μ > 2. If X is geometric with parameter p, 0 < p < 1,
denoted by g(n, p), then μ =
1−p
p and 2 =
1−p
p2 ; clearly, μ < 2. Finally if X is a Poisson
random variable with parameter , denoted by P(), then μ = 2 = . The equality of the mean
and variance of the Poisson distribution make it a very rich example in inference. The Poisson
example, if used properly in classrooms, can give a deep intuitive understanding of some of the
ideas in statistical inference. In the next section, we discuss some of these interesting results.
1. IntroductionThe Poisson probability distribution is believed to be one of the three most important distributions,the other two being the binomial and the normal distribution. The mean, μ, and variance,2, are usually the main features of a given distribution. The mean is a measure of central tendency,while the variance is a measure of the dispersion, spread or variability of a distribution. IfX is binomial with parameters n, a positive integer, and p, 0 < p < 1, denoted by b(n, p), thenμ = np and 2 = np(1 − p); clearly, μ > 2. If X is geometric with parameter p, 0 < p < 1,denoted by g(n, p), then μ =1−pp and 2 =1−pp2 ; clearly, μ < 2. Finally if X is a Poissonrandom variable with parameter , denoted by P(), then μ = 2 = . The equality of the meanand variance of the Poisson distribution make it a very rich example in inference. The Poissonexample, if used properly in classrooms, can give a deep intuitive understanding of some of theideas in statistical inference. In the next section, we discuss some of these interesting results.
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