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Chapter 8: Q 8.40 (page 330)
Suppose that you have obtained data by taking a random sample from a population. Before performing a statistical inference, what should you do?
Sample data should be examined various graphical representations.
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A variable of a population has a normal distribution. Suppose that you want to find a confidence interval for the population mean.
a. If you know the population standard deviation, which procedure would you use?
b. If you do not know the population standard deviation, which procedure would you use?
A simple randoes sample is taken from a population and yields the following data for a variable of the population:
find a point estimate for the population standard deviation (i.e., the standard deviation of the variable).
One-Sided One-Mean z-Intervals. Presuming that the assumptions for a one-mean z-interval are satisfied, we have the following formulas for -level confidence bounds for a population mean \(\mu\) :
- Lower confidence bound:
- Upper confidence bound:
Interpret the preceding formulas for lower and upper confidence bounds in words.
Bicycle Commuting Times. A city planner working on bikeways designs a questionnaire to obtain information about local bicycle commuters. One of the questions asks how long it takes the rider to pedal from home to his or her destination. A sample of local bicycle commuters yields the following times, in minutes. 
a. Find a confidence interval for the mean commuting time of all local bicycle commuters in the city. (Note: The sample mean and sample standard deviation of the data are minutes and minutes, respectively.)
b. Interpret your result in part (a).
c. Graphical analyses of the data indicate that the time of utes may be an outlier. Remove this potential outlier and repeat part (a). (Note: The sample mean and sample standard deviation of the abridged data are and , respectively.)
d. Should you have used the procedure that you did in part (a)? Explain your answer.
Explain why there is more variation in the possible values of the studentized version of than in the possible values of the standardized version of
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