lec7 - STATISTICS 13 STATISTICS Oct. 8, 2010 Lecture 7...

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STATISTICS 13 STATISTICS 13 STATISTICS 13 Lecture 7 Lecture 7 Oct. 8, 2010 Oct. 8, 2010
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Review Properties of mean and standard deviation Empirical Rule
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What does Empirical Rule Tell Us? If data is about Bell shaped, then most of the measurements lie within two standard deviations from their mean Approximation of standard deviation: when data is about bell-shaped, then 4 R s
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Tchebysheff’s Theorem Given n measurements, and an integer k greater than 1, the proportion of measurements that are within k standard deviations from the mean of the measurements is at least 1 – 1/k 2 Applies both for a sample and a population and regardless of the shape of the distribution Example:
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Example In 1999, the average time spent online was about 14 hours per person per year. Suppose that the standard deviation of the distribution of x-- the number of hours per person per year spent online, was 20 hours. Questions: - Why do you suppose the yearly average for the entire U.S. population was so low in 1999? -Do you think the distribution is relatively bell- shaped, skewed right, or skewed left? -Within what limits would you expect at least 3/4 of the measurements to lie?
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Answers: - Although some people spent a large number of hours per year online, a large majority of the population never used the Internet in 1999. Hence, there were many zero values in the population. -
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This note was uploaded on 11/18/2010 for the course STA 13 taught by Professor Samaniego during the Spring '10 term at UC Davis.

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lec7 - STATISTICS 13 STATISTICS Oct. 8, 2010 Lecture 7...

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