Intro Methods in Pol Science
Intro Methods in Pol Science POL 199
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This 2 page Class Notes was uploaded by Jammie Dare IV on Thursday October 29, 2015. The Class Notes belongs to POL 199 at Wellesley College taught by Hahrie Han in Fall. Since its upload, it has received 9 views. For similar materials see /class/230920/pol-199-wellesley-college in Political Science at Wellesley College.
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Date Created: 10/29/15
POL 199 Basic Rules of Probability De nitions 1 Random a Doing something at random means that all the outcomes have an equal chance of being the outcome 2 Conditional Probability a A conditional probability is one in which there is a restriction on something happening rst for example what is the probability that the second card drawn from a deck of cards is a queen of hearts given that the rst card is not a queen of hearts b This is written as P2nd card is queen of hearts I lst card is not queen of hearts The vertical line is read as quot given thatquot 3 Independence a Two things are independent if the chances for the second given the rst are the same no matter how the rst one turns out b Otherwise the two things are dependent c Drawing at random with replacement means that the draws are independent Drawing without replacement means that the draws are dependent 4 Mutually Exclusive a Two things are mutually exclusive when the occurrence of one prevents the occurrence of the other in other words one excludes the other 5 What is the difference between mutually exclusive and independent a Two events are mutually exclusive if the occurrence of one prevents the other from happening b Two events are independent if the occurrence of one does not change the chances for the other Rules of Probability l Multiplication Rule a The chance that two things will both happen equals the chance that the rst will happen multiplied by the chance that the second will happen given that the rst has happened b If two things are independent the chance that both will happen is the product of their unconditional probabilities 2 Addition Rule a To nd the chance that at least one of two things will happen check to see if they are mutually exclusive If they are then you add the chances 3 When do I add and when do I multiply a Addition i The addition rule nds the chance that at least one of two things will happen either A or B ii Adding the probabilities requires them to be mutually exclusive b Multiplication ii39 The multiplication rule nds the chance that two things will both happen both A and B Multiplying the unconditional probabilities of two events requires them to be independent
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