Chapter 3: Dr. Patel is concerned about the long wait times in his office. The following table presents six random observations for the patient waiting times over a period of 12 days.

	Observations (mins)
Day	1	2	3	4	5	6
1	21	27	32	25	30	29
2	22	33	30	31	27	34
3	20	29	26	24	32	30
4	32	32	21	34	28	29
5	34	26	35	27	30	26
6	35	30	29	30	31	27
7	38	36	42	35	40	32
8	35	29	30	25	28	30
9	22	25	26	30	36	28
10	26	26	34	34	25	36
11	29	26	20	31	32	33
12	28	22	/24	27	32	31

1. Dr. Patel is willing to use three-sigma limits. Use the given data and the factors from Table 3.1 (page 110) to construct R-chart and x -chart.
2. Interpret your charts. Are the process mean and process variability in statistical control?

c. The patient surveys indicate that they are willing to wait between 10 and 30 minutes before seeing Dr. Patel. Calculate the process capability index and capability ratio at the three-sigma level. Is the process capable of meeting this demand at the three-sigma level?

Table 3.1

size of sample Factor for UCL and LCL for x- chart (A2) Factor for LCL for RChart (D3) Factor for UCL for R-Chart (D4)

2	1.880	0	3.267
3	1.023	0	2.575
4	0.729	0	2.282
5	0.577	0	2.115
6	0.483	0	2.004
7	0.419	0.076	1.924
8	0.373	0.136	1.864
9	0.337	0.184	1.816
0.308	0.308	0.223	1.777