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sta 2006 0708_chapter_7

# sta 2006 0708_chapter_7 - non-normal How large a sample...

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STA 2006 Sample Size Determination (Section 6.8) 2007-2008 Term II 1 Normal Case Example 1 : A supermarket manager wishes to make an estimate of the average time in minutes a customer spends at the checkout counter. It is known from previous studies that the variance is 8.5 and the population distribution is normal. How large a sample is required if she wants a 95% conﬁdence interval for the population mean that extends no further than 0.6 minutes from the sample mean? (0.6 is denoted as ε on p. 387 of the textbook and is called the maximum error of the estimate .) 2 Non-normal Case Example 2: A research worker wishes to estimate the mean of a population using a sample large enough that the probability will be 0.95 that the sample mean will not diﬀer from the population mean by more than 22% of the standard deviation. Assume that the population distribution is
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Unformatted text preview: non-normal. How large a sample should the research worker select ? 3 Proportion Case Example 3: A cable television company would like to estimate the proportion of its customers who would purchase a fancy cable television guide. The company would like to have a 95% conﬁdence that its estimate is correct within ± . 05 from the true proportion. 1. What sample size is needed ? 2. Given the past experience in other areas indicates that roughly 30% of the customers will purchase the program guide, what sample size is needed ? 3. Given the past experience in other areas indicates that less than 20% of the customers will purchase the program guide, what sample size is needed ? 1...
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