PSYC 210 - Sampling Distributions Class Notes

PSYC 210 - Sampling Distributions Class Notes - Sampling...

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Let’s use the means we obtained from these samples of n =2 and construct a frequency distribution of means. This is called the sampling distribution of the mean: Sampling Distributions Sampling distribution: Theoretical distribution that shows the frequency of each possible value of the statistic from sample size n when 1) the null hypothesis is true and 2) the population has been sampled randomly, with replacement, until all possible samples have been taken. Example 1. Population with only five scores: 3, 4, 5, 2, 6 ( μ = 4). Sketch this distribution below using a histogram. Now let’s randomly select samples of 2 scores (n = 2) from this population until all possible samples have been taken. The two scores listed under sample scores are the samples of size 2. A mean is computed for each sample. Sample Scores M M f 3+3 3 6 1 3+4 3.5 5.5 2 3+5 4 5 3 3+2 2.5 4.5 4 3+6 4.5 4 5 4+3 3.5 3.5 4 4+4 4 3 3 4+5 4.5 2.5 2 4+2 3 2 1 4+6 5 25 = N 5+3 4 Notice: 5+4 4.5 μ M = 4 μ M = mean of the sample means 5+2 3.5 σ M = 1.02 σ M = std. dev. of the sample means 5+5 5 5+6 5.5 Sketch this distribution of means: 2+2 2 2+3 2.5 2+4 3 2+5 3.5 2+6 4 6+3 4.5 6+4 5 6+5 5.5 6+6 6 6+2 4 Dr. Viji Sathy, Psychology 210 Class Notes, 1
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Sampling distributions are used to determine probability. If we select two scores at random from the population, what is the probability that this sample will have a mean of 3.5 to 4.5? If we select two scores at random from the population, what is the probability that this sample will have a mean of 5.5 or greater? Important Concepts Related to Sampling Distributions 1. Expected value: Mean of the sample statistics; mean of the sampling distribution. If a statistic is unbiased, then the expected value = value of the parameter For the sampling distribution of the mean: μ M = μ 2. Sampling error: Difference between the sample statistic and the population parameter 3. Standard error: Average difference between sample statistic and population parameter
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This note was uploaded on 02/23/2012 for the course PSYC 210 taught by Professor Chow during the Fall '08 term at UNC.

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PSYC 210 - Sampling Distributions Class Notes - Sampling...

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