In the previous post about the Poisson approximation to the binomial distribution, we said that "since

`n`

is large and `p`

is small":I wanted to take a look at the accuracy of the approximation. In the plot at the top, p varies from 0.005 to 0.03 as shown on the x-axis, for values of n in the series 10,30,100,300 (red, blue, purple, gray). The first thing to observe is that, if

`p`

is small, the approximation is very good. The error is < 1% for all values of p < 0.25 if n is equal to 10 or 30. However, it is not necessary that n be large. In fact, the error is much worse for n = 100 or 300. Still, for 100 trials with p = 0.01, the error is < 1%.R code: