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 219 people 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 | 18.31 | 25.11 |
Mass merchandisers | 32.22 | 33.68 |
Pharmacies | 48.76 | 35.40 |
We do not know the population standard deviations, but a sample standard deviation s from so large a sample is usually close to σ. Use s in place of the unknown σ in this exercise.
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 | (_,_) |
At α = 0.10, two tailed critical value, zc = NORM.S.INV(0.10/2) = 1.645
For food stores:
x̅ = 18.31, σ = 25.11, n = 219
90% Confidence interval :
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For Mass merchandisers:
x̅ = 32.22, σ = 33.68, n = 219
90% Confidence interval :
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For Pharmacies:
x̅ = 48.76, σ = 35.50, n = 219
90% Confidence interval :
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