Probability and Statistics Probability a measure of the likelihood that an event will occur OR Probability a number expressing the likelihood that a specific event will occur expressed as the ratio of the number of actual occurrences to the number of possible occurrences P of ACTUAL occurrences of POSSIBLE occurrences o P 0 impossible for the event to occur o P 1 certain that the event will occur o P 0 5 just as likely that it will occur as that it won t occur o P 0 999999 extremely likely but not certain that the event will occur Two Types of Statistics Descriptive Statistics vs Inferential Statistics Descriptive Statistics methods of organizing and summarizing data graphs charts tables averages o Mean o Median o Mode the average number of a set the number in the direct middle of a set the number in a set that occurs most often Inferential Statistics methods used for making inferences about a population based on information obtained from a sample of the population the set of all items that are being considered in a statistical o Population investigation making statistical inferences about the population o Sample a set of items selected from a population for the purpose of Random Sample a set of items that have been selected from a population in such a way that each item of the population has an equal probability of being included in the sample
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