Learning Materials
Features
Discover
Chapter 6: Q7E (page 339)
Explain the difference between an interval estimator and a point estimator for
A random variable is an estimator, as well as a value, is an estimation that represents the estimator's calculated number.
Over 30 million students worldwide already upgrade their learning with 91影视!
All the tools & learning materials you need for study success - in one app.
Get started for free
College dropout study. Refer to the American Economic Review (December 2008) study of college dropouts, Exercise 2.79 (p. 111). Recall that one factor thought to influence the college dropout decision was expected GPA for a student who studied 3 hours per day. In a representative sample of 307 college students who studied 3 hours per day, the mean GPA was and the standard deviation was . Of interest is, the true mean GPA of all college students who study 3 hours per day.
a. Give a point estimate for .
b. Give an interval estimate for . Use a confidence coefficient of .98.
c. Comment on the validity of the following statement: 鈥�98% of the time, the true mean GPA will fall in the interval computed in part b.鈥�
d. It is unlikely that the GPA values for college students who study 3 hours per day are normally distributed. In fact, it is likely that the GPA distribution is highly skewed. If so, what impact, if any, does this have on the validity of inferences derived from the confidence interval?
Question: A random sample of n measurements was selected from a population with unknown meanand known standard deviation. Calculate a 95% confidence interval forfor each of the following situations:
a. n = 75, = 28,= 12
b. n = 200, = 102, = 22
c. n = 100, = 15,=.3
d. n = 100, = 4.05, = .83
e. Is the assumption that the underlying population of measurements is normally distributed necessary to ensure the validity of the confidence intervals in parts a鈥揹? Explain.
U.S. Postal Service鈥檚 performance. The U.S. Postal Service (USPS) reports that 95% of first-class mail within the same city is delivered on time (i.e., within 2 days of the time of mailing). To gauge the USPS performance, Price Waterhouse monitored the delivery of first-class mail items between Dec. 10 and Mar. 3鈥攖he most difficult delivery season due to bad weather conditions and holidays. In a sample of 332,000 items, Price Waterhouse determined that 282,200 were delivered on time. Comment on the performance of USPS first-class mail service over this time period.
Corporate sustainability of CPA firms. Refer to the Business and Society (March 2011) study on the sustainability behaviors of CPA corporations, Exercise 6.12 (p. 339). Recall that the level of support for corporate sustainability (measured on a quantitative scale ranging from 0 to 160 points) was obtained for each in a sample of 992 senior managers at CPA firms. The accompanying Minitab printout gives 90% confidence intervals for both the variance and standard deviation of level of support for all senior managers at CPA firms.
a. Locate the 90% confidence interval for on the printout. Interpret the result. b. Use the sample variance on the printout to calculate the 90% confidence interval for. Does your result agree with the interval shown on the printout?
c. Locate the 90% confidence interval for on the printout.
d. Use the result, part a, to calculate the 90% confidence interval for. Does your result agree with the interval shown on the printout?
e. Give a practical interpretation of the 90% confidence interval for.
f. What assumption about the distribution of level of support is required for the inference, part e, to be valid? Is this assumption reasonably satisfied? (Use your answer to Exercise 4.125, p. 270.)
Findfor each of the following:
a.= .10
b.= .01
c.= .05
d.= .20
What do you think about this solution?
We value your feedback to improve our textbook solutions.
Explanations 
Textbooks 
Flashcards 
91影视 AI 
Notes 
Study Plans 
Study Sets 
Find a degree 
Magazine