Market share for rudybird diskettes

Question

Discuss the below:

Control Charts

Researchers at Miami University in Oxford, Ohio, investigated the use of p charts to monitor the market share of a product and to document the effectiveness of marketing promotions. Markt 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 in-control process, then the company's share in the marketplace is deemed to be stable and consistent over time. In the example given in the article, the RudyBird Diskette Company collected daily sales data from a nationwide retail audit service. The first 30 days of data in the accompanying table (file rudybird.xls) indicate the total number of cases of computer disks sold and the number of RudyBird diskettes 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 prommotion would result in special cuase 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 Diskettes.

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

Day	Total Cases	RudyBird
1	154	35
2	153	43
3	200	44
4	197	56
5	194	54
6	172	38
7	190	43
8	209	62
9	173	53
10	171	39
11	173	44
12	168	37
13	184	45
14	211	58
15	179	35
16	177	56
17	143	43
18	200	69
19	134	38
20	192	47
21	155	45
22	135	36
23	189	55
24	184	44
25	170	47
26	178	48
27	167	42
28	204	71
29	183	64
30	169	43
31	201	92
32	177	76
33	205	85
34	199	90
35	187	77
36	168	79
37	198	97