Accuracy of price scanners at Wal-Mart. Refer to Exercise and the study of the accuracy of checkout scanners at Wal-Mart Stores in California. Recall that the National Institute for Standards and Technology (NIST) mandates that, for every 100 items scanned through the electronic checkout scanner at a retail store, no more than 2 should have an inaccurate price. A study of random items purchased at California Wal-Mart stores found that 8.3% had the wrong price ( Tampa Tribune , Nov. 22, 2005). Assume that the study included 1,000 randomly selected items.
a. Identify the population parameter of interest in the study.
b. Set up H0 and Ha for a test to determine whether the true proportion of items scanned at California Wal-Mart stores exceeds the 2% NIST standard.
c. Find the test statistic and rejection region (at α =.05) for the test.
d. Give a practical interpretation of the test.
e. What conditions are required for the inference made in part d to be valid? Are these conditions met?
Scanning errors at Wal-Mart. Refer to the National Institute for Standards and Technology (NIST) study of the accuracy of checkout scanners at Wal-Mart stores in California, presented in Exercise. NIST sets standards so that no more than 2 of every 100 items scanned through an electronic checkout scanner can have an inaccurate price. Recall that in a sample of 60 Wal-Mart stores, 52 violated the NIST scanner accuracy standard ( Tampa Tribune , Nov. 22, 2005). Suppose you want to estimate the true proportion of Wal-Mart stores in California that violate the NIST standard.
a. Explain why the large-sample methodology of Section 7.4 is inappropriate for this study.
b. Determine the number of Wal-Mart stores that must be sampled in order to estimate the true proportion to within .05 with 90% confidence, using the large-sample method.
Scanning errors at Wal-Mart. The National Institute of Standards and Technology (NIST) mandates that for every 100 items scanned through the electronic checkout scanner at a retail store, no more than 2 should have an inaccurate price. A recent study of the accuracy of checkout scanners at Wal-Mart stores in California ( Tampa Tribune , Nov. 22, 2005) showed that, of the 60 Wal-Mart stores investigated, 52 violated the NIST scanner accuracy standard. If 1 of the 60 Wal-Mart stores is randomly selected, what is the probability that that store does not violate the NIST scanner accuracy standard?
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