Johnsons assembly unit has decided to use a pChart with 2sig

Johnson\'s assembly unit has decided to use a p-Chart with 2-sigma control limits to monitor the proportion of defective steel bars produced by their production process. The quality control manager randomly samples 150 steel bars at 16 successively selected time periods and counts the number of defective steel bars in the sample. See sample data table below.

Please construct a control chart using the sample data below. What is the upper, center, and lower control limits? And what value of z should be use to construct the chart? Please round answers to at least 3 decimal places.

Sample	Defects
1	7
2	7
3	8
4	9
5	7
6	10
7	9
8	7
9	8
10	10
11	12
12	10
13	11
14	13
15	12
16	8

Solution

p Chart Summary Intermediate Calculations Sum of Subgroup Sizes 2400 Number of Subgroups Taken 16 Average Sample/Subgroup Size 150 Average Proportion of Nonconforming Items 0.06166667 Two Standard Deviations 0.03928151 Preliminary Lower Control Limit 0.02238516 p Chart Control Limits Lower Control Limit 0.022 Center 0.062 Upper Control Limit 0.101