# Probability - Introduction The emphasis in Chapters 2 3 and...

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Introduction The emphasis in Chapters 2, 3 and 4 is on descriptive statistics . In those chapters we described methods used to collect, organize, and present data, as well as measures of central location, dispersion, and skewness used to summarize data. A second facet of statistics deals with computing the chance that something will occur in the future. This facet of statistics is called inferential statistics . An inference is a generalization about a population based on information obtained from a sample. Probability plays a key role in inferential statistics. It is used to measure the reasonableness that a particular sample could have come from a particular population. What is Probability? Probability allows us to measure effectively the risks in selecting one alternative over the others. In general, it is a number that describes the chance that something will happen. Probability : A value between zero and one, inclusive, describing the relative possibility (chance or likelihood) an event will occur. Probability is expressed either as a percent or as a decimal. The likelihood that any particular event will happen may assume values between 0 and 1.0. A value close to 0 indicates the event is unlikely to occur, whereas a value close to 1.0 indicates that the event is quite likely to occur. To illustrate, a value of 0.60 might express your degree of belief that tuition will be increased at your college, and 0.50 the likelihood that your first marriage will end in divorce. In our study of probability we will make extensive use of several key words. They are: experiment, outcome , and event . Experiment : A process that leads to the occurrence of one and only one of several possible observations. For example, you roll a die and observe the number of spots that appear face up. The experiment is the act of rolling the die. Your survey company is hired by Ford to poll consumers to determine if they plan to buy a new American made car this year. You contact a sample of 5,000 consumers. The act of counting the consumers who indicated they would purchase an American made car is the experiment. Outcome : A particular result of an experiment. One outcome of the die rolling experiment is the appearance of a 6. In the experiment of counting the number of consumers who plan to buy a new American-made car this year, one possibility is that 2,258 plan to buy a car. Another outcome is that 142 plan to buy one. Event : A collection of one or more outcomes of an experiment. Thus, the event that the number appearing face up in the die rolling experiment is an even number is the collection of the outcomes 2, 4, or 6. Similarly the event that more than half of those surveyed plan to buy a new American made car is the collection of the outcomes 2,501, 2,502, 2,503, and so on all the way up to 5,000. Approaches To Probability

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Probability - Introduction The emphasis in Chapters 2 3 and...

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