Question

The data below give the number of lot-to-lot failures of a plastic-encapsulated resistor to a moisture-resistance test.

Subgroup Number	Number of Non-conforming	Subgroup Size
1	8	250
2	5	125
3	3	125
4	6	210
5	18	250
6	1	150
7	4	125
8	1	125
9	5	150
10	3	250
11	2	150
12	10	250
12	6	125
14	3	125
15	6	150
16	11	125
17	4	125
18	4	125
19	2	150
20	4	210
21	8	150
22	2	150
23	3	150
24	6	125
25	6	210
26	6	125
27	5	150
28	5	125
29	3	150
30	6	150

1. What type of attribute control chart should be used for process monitoring for this application and why?
2. Set up the control chart with exact limits (state the exact formulas used to compute the control limits). Plot the preliminary data and state which subgroups (samples) are identified as being out of control? What is the major disadvantage of using this type of chart in practice?

Answer 1