Poisson

• Poisson - a distribution for discrete data, denoted by λ.
• Poisson conditions


  Randomly occurring events

  Independent events

  Constant average rate (λ)
• mean = λ
• variance = λ
• How do we find exact probabilities ?

  Poisson PD
• How do we find cumulative probabilities?


  Poisson CD
• Spotting poisson


  Very likely to be hidden in a question, mainly look out for the constant average rate.
• Exam technique for poisson


  • can be combined with other distributions
  • if asked to explain why it is a suitable / not model you must refer to the 3 conditions on CONTEXT
  • mean ≈ variance
  • has no end value - can take all positive integers
  • poisson distributions can be combined together, if independent