1. MA 102 Statistical Controversies Monday, April 1, 2002 Today: Randomness and probability Probability models and rules Reading (for Wednesday): Chapter 18: Probability models Exercises: 18.3, 18.5, 18.8, 18.10, 18.13, 18.15. Reminder: Test #2 is on Friday

2. Probability Models A probability model for a random event is a description of all the possible outcomes and an assignment of probabilities to those outcomes.

3. Types of Probability Models Two basic types: When there are a relatively small number of possible outcomes, a discrete model lists all the individual probabilities. For example, roll two dice. When there are a large number of possible outcomes, a density curve model assigns probabilities to groups of outcomes. For example: sampling distributions.

4. Probability Rules A. Every probability is between 0 and 1. B. All possible outcomes together must have probability 1. C. The probability that an outcome does not occur is 1 – the probability that it does. D. If two outcomes have nothing in common, then the probability that one or the other occurs is the sum of their individual probabilities.