Researchers at Miami University in Oxford, Ohio, investigated the use of p charts Ohio to monitor the market share of a product and to document the effectiveness of marketing share of a product and to document the effectiveness of marketing promotions. Marketing share is defined as the company's proportion of the total number of products sold in a category. If a p chart based on a company's market share indicates an incontrol process, then the company's share in the market-place is deemed to be stable and consistent over time. In the example givenin the article, the RudyBird Disk Company collected daily sales data from a nationwide retail audit service. The first 30 days of data in the accompanying table below indicate te total number of cases of computer disks sold and the number of RudyBird disks sold. The final 7 days of data were taken after RudyBird launched a major in-store promotion. A control chart was used to see if the in-store promotion would result in special cause variation in the marketplace.

a. Construct a p chart using data from the first 30 days (prior to the promotion) to monitor the market share for RudyBird Disks.

b. Is the market share for RudyBird in control before the start of the in-store promotion?

c. On your control chart, extend the control limits generated in (b) and plot the proportions for days 31 through 37. What effect, if an, did the in-store promotion have on RudyBird's market share?