STATS PRELIM 2 NOTES

# STATS PRELIM 2 NOTES - Relative Frequencies Number of...

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Relative Frequencies Number of Outcome A / Total # Probability (A) General Addition Rule – Add the probabilities of two events and then subtract out the probability of their intersection. This does not require disjoint events. For any two events, A and B, the probability of A or B is P(A or B) = P(A) + P(B) – P(A and B) Conditional Probability –It takes into a account a given condition. To find P(B|A), or the probability of B given A, restrict attention to the outcomes in A. Then find what fraction of those outcomes B also occurred. P(B|A) = P(A and B) / P(A) General Multiplication Rule – Rule for compound events that don’t require the events to be independent. P(A and B) = P(A) x P(B|A) Independence – Events A and B are independent if (and only if) the probability of A is the same when we are given that B has occurred. Or, the outcome of one event does not influence the probability of the other. That is: P(A) = P(A|B) 1. DISJOINT EVENTS ARE NEVER INDEPENDENT! Disjoint = Events have NO outcomes in common Sampling Distribution Model - Different random samples give different values for a statistic. The sampling distribution model shows the behavior of the statistic over all the possible samples for the same size “n”. 1. How is the mean of the sampling distribution related to the mean of the population? - Mean of sampling distribution should equal mean of population 2. How is the SD of the sampling distribution related to the SD of the population? - SD of sampling distribution = SD of population / square root (n) 3. How is the shape of the sampling distribution affected by the sample size? - Becomes more normal as “n” increases Sampling Distribution Model for a Proportion - If assumptions of independence and random sampling are met, and we expect at least 10 successes and 10 failures, then the sampling distribution of a proportion is

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## This note was uploaded on 05/10/2008 for the course ILRST 2100 taught by Professor Vellemanp during the Spring '07 term at Cornell.

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STATS PRELIM 2 NOTES - Relative Frequencies Number of...

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