Normative Rules

Normative Rules of Probability Calculus

  1. Probabilities are always positive, or equal to 0.
  2. The probability of an event plus the probability of its opposite must always equal 1 (because the event either happens or it doesn't.)
  3. The probability of an event A is always greater than or equal to the probability of an event A and an event B.
    For example, if you choose a person at random, you have a better chance of choosing a woman than you have of choosing a woman with dark hair.

Normative Rules for Statistics (Sampling)

  1. The more people we survey, the more accurate the result. Larger samples are better. (This is known as the Law of Large Numbers.)
  2. Random processes are not self-correcting.
    For example, if you do a survey of children's intelligence and the first child you survey happens to have an IQ of 150, the result will be higher than average. Many people think that, if you survey 9 more children, the sample will still give average intelligence -- but this is simply not true. Why should the next 9 children surveyed all have lower than average IQs?

- Probability quiz.
- Numbers for the real world: The numeracy page.
- Some guidelines for 'quick check' calculations.
- Some useful number facts for quick checks.
- Return to the front gate of Esmerel.

Page maintained by the Mathemagician.