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Unformatted text preview: Sampling Distributions for Sample Means IPS Chapter 5.2 2009 W.H. Freeman and Company Objectives (IPS Chapter 5.2) Sampling distribution of a sample mean The mean and standard deviation of For normally distributed populations The central limit theorem Weibull distributions x Reminder: What is a sampling distribution? The sampling distribution of a statistic is the distribution of all possible values taken by the statistic when all possible samples of a fixed size n are taken from the population. It is a theoretical idea we do not actually build it. The sampling distribution of a statistic is the probability distribution of that statistic. Sampling distribution of the sample mean We take many random samples of a given size n from a population with mean and standard deviation . Some sample means will be above the population mean and some will be below, making up the sampling distribution. Sampling distribution of x bar Histogram of some sample averages Sampling distribution of x bar / n For any population with mean and standard deviation : The mean , or center of the sampling distribution of , is equal to x Mean of a sampling distribution of There is no tendency for a sample mean to fall systematically above or below , even if the distribution of the raw data is skewed. Thus, the mean of the sampling distribution is an unbiased estimate of the population mean it will be correct on average in many samples. Standard deviation of a sampling distribution of The standard deviation of the sampling distribution measures how much the sample statistic varies from sample to sample. It is smaller than the standard deviation of the population by a factor of n . x x For normally distributed populations When a variable in a population is normally distributed, the sampling distribution of for all possible samples of size...
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This note was uploaded on 04/25/2009 for the course ECON 41 taught by Professor Guggenberger during the Winter '07 term at UCLA.
 Winter '07
 Guggenberger

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