Poisson distribution notation

The binomial distribution notation is to write X\sim B(n, p). This means:

• X is a discrete random variable
• X follows a binomial distribution - shown by the B
• n is the number of trials
• p is the probability of success on each trial

The notation for a poisson distribution is very similar. We can write X\sim P(\lambda), which means:

• X is a discrete random variable
• X follows a poisson distribution - shown by the P
• \lambda is the mean number of successes in the given time period (or area, etc.)

This isn’t so common though, because the P may be confused with a probability. to get around that, we usually write Po instead of P:

X\sim Po(\lambda)