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Unformatted text preview: Probability Introduction An experiment is an act of observation that leads to a single outcome that cannot be predicted with certainty. An event is a specific collection of sample points. A sample point (or simple event) is the most basic outcome of an experiment. Sample point ~ outcome A sample space (denoted S) is the collection of all possible outcomes of an experiment. Examples: List the different possible families that can occur when a couple has three children… List the possible outcomes for three flips of a fair coin… The probability of an event A is calculated by summing the probabilities of the sample points in the sample space for A. ( ) n P A N = , n = # of times you observed event A (number of ways A can happen), N = number of observations (Number of total possibilities). Example: Using the sample space created above for having three children, find the probability of having at least two girls. Probability Rules for Sample Points: 1. All sample point probabilities must be between 0 and 1. 2. The sum of the individual sample point probabilities must be equal to 1. Example: Use the data summarized below to determine the probability that a subject did not use marijuana. Also, find the probability of a false – positive. Did the subject use marijuana? Yes No Totals Positive test result 119 24 143 Negative test result 3 154 157 Total 122 178 300 The Union of two events is the event that A or B or Both occur on a single performance...
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 Fall '08
 STAFF
 Conditional Probability, Probability, Probability theory

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