Question

Another defect type you would like to control using appropriate SPC technique is
appearance of stain in the round neck shirts. You obtain the following data:

Sample # of stain in size the shirts SUBGROUP .com/webapps/assessment/review/review.jsp?attempt id_3 Review Test Submission: CO 400 390 15 400 10 390 8 400 7 405 9 400 10 410 12 410 13 405 14 2 4 6 10

a. How many set of upper control limits and lower control limits have to be
calculated?
b. Compute for the center line and Upper Control limit and also Lower control limit
c. Is the process operating in statistical control?[Why?

Answer 1

a) We have to calculate the upper control limit(UCL) and lower control limit (LCL) for each subgroup. Here 4 distinct subgroups with size 400,390,405 and 410 are given, so we need to calculate four set of upper control limit and lower control limit.

b) Refer the table in images.

c) Here, the number of strains per 100 sample i.e. $u_{_{i}}$ lies between LCL(Lower Control Limit) and UCL (Upper Control Limit) for each subgroup, so the process is operating in statistical control.