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Copyright © 1998, Triola, Elementary Statistics Addison Wesley Longman 1 Probability Distributions Chapter 4 M A R I O F. T R I O L A Copyright © 1998, Triola, Elementary Statistics Addison Wesley Longman
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Copyright © 1998, Triola, Elementary Statistics Addison Wesley Longman 2 Overview This chapter will deal with the construction of probability distributions by presenting possible outcomes along with relative frequencies we expect.
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Copyright © 1998, Triola, Elementary Statistics Addison Wesley Longman 3 Chapter 4 Probability Distributions 4-1* Overview 4-2 Random Variables 4-3 & 4-4 Binomial Experiments 4-5* The Poisson Distribution
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Copyright © 1998, Triola, Elementary Statistics Addison Wesley Longman 4 4-2 Random Variables
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Copyright © 1998, Triola, Elementary Statistics Addison Wesley Longman 5 Example: 10 balls marked 0 to 9 and placed in a box. Pick one ball out from the box. Q: How to represent the outcome (i.e., the number on that ball)? Solution: Use a variable, say x, to represent the outcome ----- x is called a random variable Two meanings: (1) x is one of the 10 possible outcomes: 0,1, …, 9 (2) Each can happen with a positive chance
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Copyright © 1998, Triola, Elementary Statistics Addison Wesley Longman 6 Definitions Random Variable a variable (usually x ) that has a single numerical value (determined by chance) for each outcome of an experiment Discrete random variables have a finite number or countable number of values. Continuous random variables have infinitely many values which can be associated with measurements on a continuous scale with no gaps or interruptions.
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Copyright © 1998, Triola, Elementary Statistics Addison Wesley Longman 7 Definitions Probability Distribution gives the probability for each value of the random variable
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Copyright © 1998, Triola, Elementary Statistics Addison Wesley Longman 8 Probability Distribution for Number of USAir Crashes Among Seven 0123456701234567 0.210 0.367 0.275 0.115 0.029 0.004 0+ x P(x)P(x) Table 4-1
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Copyright © 1998, Triola, Elementary Statistics Addison Wesley Longman 9 Probability Histogram 0.40 0.30 0.20 0.10 0 0 1 2 3 4 5 6 7 Probability Histogram Number of USAir Crashes Among Seven Figure 4-3 Number of USAir Crashes Among Seven Probability
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Copyright © 1998, Triola, Elementary Statistics Addison Wesley Longman 10 Requirements for Probability Distribution
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Copyright © 1998, Triola, Elementary Statistics Addison Wesley Longman 11 Requirements for Probability Distribution P ( x ) = 1 where x assumes all possible values
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Copyright © 1998, Triola, Elementary Statistics Addison Wesley Longman 12 Requirements for Probability Distribution P ( x ) = 1 where x assumes all possible values 0 P ( x ) 1 for every value of x
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Copyright © 1998, Triola, Elementary Statistics Addison Wesley Longman 13 Formula 4-1 Mean: µ = x P (x) Formula 4-2 Variance: 2 = [ (x – µ) 2 P(x )] Formula 4-3 2 = [ x 2 P (x )] – µ 2 (shortcut) Mean, Variance and Standard Deviation of a Probability Distribution
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Copyright © 1998, Triola, Elementary Statistics Addison Wesley Longman 14 Mean, Variance and Standard Deviation of a Probability Distribution Formula 4-1 Mean: µ = x P (x) Formula 4-2 Variance: 2 = [ (x – µ) 2 P(x )] 2 = [ x 2 P (x )] – µ 2 (shortcut) Formula 4-4 SD: = [ x 2 P (x )] –µ 2
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Copyright © 1998, Triola, Elementary Statistics Addison Wesley Longman 15 Round off Rule for µ, 2, and Round results by carrying one more decimal place than the number of decimal places used for the random variable x. If the values of x are integers, round µ, 2, and to one decimal place.
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Copyright © 1998, Triola, Elementary Statistics Addison Wesley Longman 16 Definition Expected Value The average value of outcomes E = [ x P( x )]
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