Question

When printing full color glossy magazine advertising pages, editors do not like to see blemished. One person at the printer looks at samples of magazine pages (n =20) and counts blemishes. Below are her results. Determine the centerline and control limits. Create a chart of this process. Give reasons as to why you think the process is either in control or not in control.

Sub Group #	Count of Defects
1	65
2	80
3	60
4	50
5	52
6	42
7	35
8	30
9	30
10	25

Answer 1

The centerline is the mean of the data given. This can be calculated by using the AVERAGE function in MSExcel. Also, the standard deviation is computed by using function STDEV in the excel.

Centerline = Average of data = 46.90

Standard Deviation = 17.79

Upper control Limit = Average + (3 * Standard Deviation) = 100.26

Lower control Limit = Average - (3 * Standard Deviation) = - 6.46

Below is the control chart of the process. The Process is in control as all the values are under 3sigma control limits.

Please Note:

Blue: Process values

Brown: Mean (Average)

Grey: Upper control limit

Orange: Lower control limit