A producer of smartphones is monitoring the quantity of defective devices, specifically those with malfunctioning screens. (a) Establish the centerline and control limits for a chart tracking the number of nonconforming smartphones. (b) Assess the process capability. (c) Assume the existence of assignable causes, and revise the chart.
Subgroup number Sample size Nonconforming
1 310 10
2 310 8
3 310 9
4 310 12
5 310 10
6 310 11
7 310 9
8 310 10
9 310 12
10 310 11
11 310 31
12 310 32
13 310 10
14 310 8
15 310 12
16 310 10
17 310 11
18 310 9
19 310 10
20 310 8