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Unformatted text preview: Chapter 7 Section 2 Confidence Intervals and Sample Size Mr. Kenneth Horwitz November 15, 2010 1 Confidence Intervals for the Mean When s Is Unknown The value of s , when it is not known, must be estimated by using s , the standard deviation of the sample. When s is used, especially when the sample size is small (less than 30), critical values greater than the values for are used in confidence intervals in order to keep the interval at a given level, such as the 95%. These values are taken from the Student t distribution , most often called the t distribution . 2 2 z α Characteristics of the t Distribution The t distribution is similar to the standard normal distribution in these ways: 1. It is bellshaped. 2. It is symmetric about the mean. 3. The mean, median, and mode are equal to 0 and are located at the center of the distribution....
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This note was uploaded on 12/09/2011 for the course STATS 221 taught by Professor Nielson during the Fall '10 term at BYU.
 Fall '10
 Nielson

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