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# Research Statistics (Psych 2040) Lecture Notes

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School
Department
Psychology
Course
PSYC 2040
Professor
David Stanley
Semester
Winter

Description
Research Statistics Lecture Summaries Lecture 1 IntroductionThe purpose of statistics is to make a conclusion about a large group of people a population from a small group of people a sample Describing the PopulationPopulation mean is an average o Ideally we would like to be able to describe the population using this population mean o However this is impractical we cannot survey everyone o This is why we use a sample mean to estimate the population mean o We are usually interested in a sample only to the extent that it tells us something about the population Population standard deviation o The larger the SD is the larger the differences o It is used to describe how accurate the mean is in describing everyone in the population o It is roughly on average the amount that a score differs from the population meanStandard error of the mean o Roughly on average the amount that sample means differ from the population mean due to the effects of random sampling o It is the amount of variability in sample means that we would expect if we used random sampling o Describes the variabilityo Larger sample sizes result in small standard errors that means there is less variabilityEstimated Standard deviation o Roughly on average the amount that a score differs from the sample mean o Based on our single sample this is our best guess of what the population standard deviation isEstimated standard error of the mean o Roughly on average the amount that a sample means differ from the population mean o Based on our single sample this is our best guess of what the Standard Error of sample means would be with repeated sampling o You can also think of SE based on your sample as our best guess of the amount of variability in sample means that we would expect if we used random sampling o Note that when researchers say Standard Error they are usually referring to Estimated Standard Error o Ratios are extremely important way of comparing 2 things in statisticsWe typically based the denominator on standard error standard error squared in these ratios Central Limit TheoremRegardless of the shape of the population distribution the distribution of sample means will o Always be roughly normal o Have a standard error equal to the population standard deviation divided by the square root of sample size
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