统计学课件（英文版）ch04.pptVIP

Slides Prepared by JOHN S. LOUCKS St. Edward抯 University Chapter 4 Introduction to Probability Experiments, Counting Rules, and Assigning Probabilities Events and Their Probability Some Basic Relationships of Probability Conditional Probability Bayes?Theorem Probability Probability is a numerical measure of the likelihood that an event will occur. Probability values are always assigned on a scale from 0 to 1. A probability near 0 indicates an event is very unlikely to occur. A probability near 1 indicates an event is almost certain to occur. A probability of 0.5 indicates the occurrence of the event is just as likely as it is unlikely. Probability as a Numerical Measureof the Likelihood of Occurrence 0 1 .5 Increasing Likelihood of Occurrence Probability: The occurrence of the event is just as likely as it is unlikely. An Experiment and Its Sample Space An experiment is any process that generates well-defined outcomes. The sample space for an experiment is the set of all experimental outcomes. A sample point is an element of the sample space, any one particular experimental outcome. Example: Bradley Investments Bradley has invested in two stocks, Markley Oil and Collins Mining. Bradley has determined that the possible outcomes of these investments three months from now are as follows. Investment Gain or Loss in 3 Months (in $000) Markley Oil Collins Mining 10 8 5 -2 0 -20 A Counting Rule for Multiple-Step Experiments If an experiment consists of a sequence of k steps in which there are n1 possible results for the first step, n2 possible results for the second step, and so on, then the total number of experimental outcomes is given by (n1)(n2) . . . (nk). A helpful graphical representation of a multiple-step experiment is a tree diagram. Example: Bradley Investments A Counting Rule for Multiple-Step Experiments Bradley Investments can be viewed as a two-step experiment; i