What you'll learn
How probabilities are spread across the possible outcomes of an experiment.
Probability distributions
- A probability distribution lists each outcome with its probability; the probabilities sum to 1.
- Can be shown as a table or diagram.
Named distributions
- Binomial distribution: a fixed number of independent trials, each a 'success' or 'failure' with constant probability (e.g. number of heads in 10 coin tosses).
- Normal distribution: a symmetric, bell-shaped distribution for continuous data, centred on the mean, with spread set by the standard deviation. Most data lies within a few standard deviations of the mean.
Exam tips
- Check the probabilities in a distribution table add to 1.
- Recognise a normal distribution from its symmetric, bell shape.
Common mistakes
- Probabilities in a distribution not summing to 1.
- Confusing discrete (binomial) with continuous (normal) data.