PSYC 210 - Probability

PSYC 210 - Probability - Probability Probability of A =...

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Probability Probability of A = p(A) = number of outcomes classified as A total number of possible outcomes Probabilities in research articles are reported as a proportion . It is common to see a probability written as being less than some number, such as p < .05 or p < . 001 Or as SPSS “sig” means p=_________ The likelihood of finding a particular statistic Two important assumptions: 1. Random sampling: Each individual in the population has an equal chance of being selected 2. Sampling with replacement: Each individual in the sample is returned to the population before another sample is drawn. This keeps probabilities constant across sampling. Why is probability important in statistics? If we know the make-up of a population we can determine the probability of obtaining specific samples. Our real goal: our goal is to do the opposite Have a sample -> make inference about population – inferential statistics Parameter = populations; statistic=sample Discrepancy between parameter and statistic is SAMPLING ERROR Example Select one card from a deck: 52 possible outcomes p(king of hearts) = 1/52 p(Aces) = 4/52 What is a probability of 1? The event occurs every time. We cannot have a probability that occurs more than 1 time. 0 is the minimum – meaning the event doesn’t occur. Probability and Distributions
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This note was uploaded on 02/23/2012 for the course WMST 101 taught by Professor Burns during the Fall '08 term at UNC.

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PSYC 210 - Probability - Probability Probability of A =...

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