Maths and Stats

Question 1

What is meant by CPK? What values are associated with stable performance?

Answer 1

CPK- ability of product to meet specification.

<1.33 incapable
>1.33 capable

Question 2

What is a 95% confidence interval?

Answer 2

Error bounds around a mean value
95% confidence interval means that you are 95% confidence the mean sits within these error bounds.

Question 3

What is the difference between CP and CPK?

Answer 3

CP- how well does capability fit with spec?
CPk- Is the mean centrally located within specification?

Question 4

What does a schewhart chart do? What are the cause rules?

Answer 4

Designed to detect special cause variation- rare events, easy to detect.

7 points rising in one direction
7 points below/above mean
Patterns of data
Any OOS

Question 5

What is common cause variation?

Answer 5

Random variation, always present and inherent to process

Question 6

What is a Cusum chart? How are they used?

Answer 6

Cumulative summation chart
Magnify gradual trends
Data either side of a mean should always ‘average out’- shows if it doesn’t

Apply a V mask to claim notable change vs expected standard deviation.

Question 7

What methods of data analysis are useful in problem solving?

Answer 7

Fishbone analysis (ishikawa)
Pareto analysis
5 why investigations