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Chapter 6

Chapter 6

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Gillian Rowe

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Chapter 6 Probability61 Introduction to ProbabilityRole of inferential stats is to use sample data as the basis for answering questions about the populationrelationships bw samples and pops are usually defined in terms of probability Ex 50 black and 50 white marbles in a jar pop and pick one sample theres a 5050 chance of getting either colourwith a jar of 90 black and 10 white though sample will probably be black knowing makeup of pop can determine probability of obtaining specific samples Probability DefinitionProbabilityfor situations where several different outcomes are possible defined as a fraction or a proportion of all possible outcomes If outcomes are identified as A B C D and so on thenprobability of Anumber of outcomes classified as Atotal number of possible outcomes PopulationProbabilitySampleSampleInferential StatisticsPopulationEx if youre selecting a card from a deck there are 52 possible outcomes probability of selecting a king of hearts is p152 probability of selecting an ace is p452For notation probability for selecting a king from a deck is written as pkingProbability values most often expressed as decimal values but can also be a fraction or All probability values contained in a range from 0 never occurs 0 to 1 always occurs 100 Random SamplingRandom sampleeach individual in the population has an equal chance of being selected and probabilities must stay constant from one selection to the next if more than one individual is selectedidentifies a simple random sampleindependent random sampleFirst requirement equal chance ensures theres no bias in the selection processFor the second requirement it demands that you sample with replacement necessary to return each individual to the population before you make the next selection Probability and Frequency DistributionsWhen a population is presented in a frequency distribution graph it is possible to represent probabilities as proportions of the graph look at example 61 page 6 62 Probability and the Normal DistributionNormal distribution is symmetrical with highest frequency in the middle and frequencies tapering off as you move toward either extreme example 62 page 9goodA distribution is normal of any only if it has all the right proportionsZscore transformation0 to 13413 1 to 21359 past 2228If were trying to determine a probability by using a normal distribution graph compute a zscore for the score ex becomes p z200228
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