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Chapter 4: Q 15. (page 227)
Random digits In using Table D repeatedly to choose random samples, you should not always begin at the same place, such as line Why not?
We shouldn't always begin from the same place.
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Sampling stuffed envelopes A large retailer prepares its customers鈥� monthly credit card bills using an automatic machine that folds the bills, stuffs them
into envelopes, and seals the envelopes for mailing. Are the envelopes completely sealed? Inspectors choose envelopes from stuffed each hour for visual inspection. Identify the population and the sample.
Do reducing diets work? Dr. Linda Stern and her colleagues recruited obese adults at the Philadelphia Veterans Affairs Medical Center in Pennsylvania. Half of the participants were randomly assigned to a low-carbohydrate diet and the other half were assigned to a low-fat diet. Researchers measured each participant鈥檚 change in weight and cholesterol level after six months and again after one year. Subjects in the low-carb diet group lost significantly more weight than subjects in the low-fat diet group during the first six months of the study. At the end of a year, however, the average weight loss for subjects in the two groups was not significantly different.
(a) Why did researchers randomly assign the subjects to the diet treatments?
(b) Explain to someone who knows little statistics what 鈥渓ost significantly more weight鈥� means.
(c) The subjects in the low-carb diet group lost an aver-age of kg in a year. The subjects in the low-fat diet group lost an average of kg. Explain how this infor-
mation could be consistent with the fact that weight loss in the two groups was not significantly different.
Close shave Which of two brands of electric razor shaves closer? Describe how you would design and carry out an experiment to answer this question using
adult male volunteers.
Sampling by accountants Accountants often use stratified samples during audits to verify a company鈥檚 records of such things as accounts receivable. The
stratification is based on the dollar amount of the item and often includes sampling of the largest items. One company reports accounts receivable. Of these, are in amounts over are in amounts between and the remaining are in amounts under Using these groups as strata, you decide to verify all the largest accounts and to sample of the midsize accounts and of the small accounts. How would you label the two strata from which you will sample? Use Table D, starting at line to select only the first accounts from each of these strata.
Attitudes toward alcohol At a party, there are students over age and students under age You choose at random 3 of those over 21 and separately choose at random of those under to interview about attitudes toward alcohol. You have given every student at the party the same chance to be interviewed: what is the chance? Why is your sample not an SRS?
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