In: Statistics and Probability
Consumers can purchase nonprescription medications at food
stores, mass merchandise stores such as Target and Wal-Mart, or
pharmacies. About 45% of consumers make such purchases at
pharmacies. What accounts for the popularity of pharmacies, which
often charge higher prices?
A study examined consumers' perceptions of overall performance of
the three types of stores, using a long questionnaire that asked
about such things as "neat and attractive store," "knowledgeable
staff," and "assistance in choosing among various types of
nonprescription medication." A performance score was based on 27
such questions. The subjects were 196people chosen at random from
the Indianapolis telephone directory. Here are the means and
standard deviations of the performance scores for the sample.
Store type | x | s |
Food stores | 18.49 | 24.97 |
Mass merchandisers | 32.55 | 33.68 |
Pharmacies | 48.74 | 35.41 |
(b) Give 90% confidence intervals for the mean performance for each type of store. (Round your answers to three decimal places.)
Food stores |
( , ) |
Mass merchandisers |
( , ) |
Pharmacies |
( , ) |
Since n is very large, we use the z distribution. The Zcritical (2 tail) for = 0.10 is 1.645
90% Confidence interval for the Food Stores:
Given: = 18.49, s = 24.97, n = 196
The Confidence Interval is given by ME, where
The Lower Limit = 18.49 - 2.934 = 15.556
The Upper Limit = 18.49 + 2.934 = 21.424
The 90% Confidence Interval is (15.556 , 21.424)
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90% Confidence interval for the Mass Merchandisers:
Given: = 32.55, s = 33.68, n = 196
The Confidence Interval is given by ME, where
The Lower Limit = 32.55 - 3.957 = 28.593
The Upper Limit = 32.55 + 3.957 = 36.507
The 90% Confidence Interval is (28.593 , 36.507)
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90% Confidence interval for the Pharmacies:
Given: = 48.74, s = 35.41 n = 196
The Confidence Interval is given by ME, where
The Lower Limit = 48.74 - 4.161 = 44.579
The Upper Limit = 48.74 + 4.161 = 52.901
The 90% Confidence Interval is (44.579 , 52.901)
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