Wal-Mart buyers seek to purchase adequate supplies of various brands of toothpaste to meet the ongoing demands of its customers. In particular, Wal-Mart is interested in estimating the proportion of its customers who favor the country’s leading brand of toothpaste, Crest. The file P8_41.XLS contains the toothpaste brand preferences of 2000 Wal-Mart customers, obtained recently through the administration of a customer survey. 

a Use Excel to choose a simple random sample of size 100 from the given frame. 

b Using the sample found in part a, compute a point estimate (called the sample proportion, p) of the true proportion of Wal-Mart customers who prefer Crest toothpaste. What is the sampling error in this case? Assume that the population consists of the preferences of all customers in the given frame. 

c. Given that the standard error of the sampling distribution of the sample proportion p is approximately compute a good approximation to the standard error of the sample proportion in this case. 

d. Repeat parts b and c after generating a simple random sample of size 50 from the given frame. How do you explain the differences in your computed results?

Transcribed Image Text:

√p(1-P)/n.