Related yet different, here’s how…

A quick note on the “preliminary terrors” of notation:

• e is Euler’s number – you’ll find the e on your calculator or the EXP() function in Excel
• The parameter is conventionally written as λ (pronounced lambda).
 Poisson Exponential Number of events that occur in an interval of time Time taken between 2 events occurring For example… the number of Metrorail trains that arrive at the platform in an hour For example… the time between one Metrorail train arriving and the next 6 trains 10 minutes between trains The random variable is discrete – this is a countable number of things that happen The random variable is continuous – typically time, but may represent other factors like distance l represents the number of events (per unit of time) l represents time between individual events Graphically, a Poisson distribution looks like this: Graphically, an Exponential distribution looks like this: Calculate probability as follows: P(X=x) = e–λλx / x! Calculate probability as follows: P(x>n) = e–λ(n) P(x

2 amazingly simple video tutorials are available on YouTube if you need a quick walk-through: