Ch 7 Sec 2

# Ch 7 Sec 2 - Chapter7 Section2 SampleSize Mr.KennethHorwitz...

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Chapter 7 Section 2 Confidence Intervals and  Sample Size Mr. Kenneth Horwitz November 15, 2010 1

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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  distribution is similar to the standard normal  distribution in these ways: 1. It is bell-shaped. 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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