AP Stats 9.3 Sample Means by Chuck Baker

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AP Stats 9.3 Sample Means

Published on Nov 19, 2015

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PRESENTATION OUTLINE

9.3 SAMPLE MEANS

PART 1: APPROXIMATING A POPULATION W/ X BAR

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Last section we saw sample proportions approximated by the normal curve when the sample was less than 10% of the population size

This section, we see the same with sample means.

Means usually arise from QUANTITATIVE data, like incomes, or the lifetime of a brakepad.

The sampling distribution of x bar is the distribution of the values of x bar in ALL possible sample of the same size from the population.

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BEHAVIOR OF X BAR IN REPEATED SAMPLES:

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1. The sample mean, xbar, is an unbiased estimator of the population mean.

2. Values of x bar are less spread for larger samples. Their SD decreases at a rate of sqrt(n), so a sample must be FOUR times larger to be HALF as spread.

3. You can only use the formula for standard deviation of sample means if the population is at least TEN times larger than the population of interest.

Chuck Baker

http://www.mrcbaker.com