Other Useful Tools for Statistical Process Control (aka “The Magnificent Seven”)

Class Schedule Today: new content (will be on exam) Tuesday, Sept 30th: Exam review Bring your formula sheet Thursday, Oct 2nd: Exam! Tuesday, Oct 7th: No class! Can attend career fair during class time I will hold office hours (5262 SAS) during class time if you have questions

Announcement: Sciences Career Fair October 7th from 10:00-3:00 at Tally careers.ncsu.edu/events-and-career-fairs/sciences-career-fair/ Notes: Dress Professionally Bring multiple copies of your resume Bring your student ID   Questions? Contact Career Development Center (919-515-2396) or Jenna Hartwell (jrhartwe@ncsu.edu)

Magnificent Seven Seven major tools for SPC Histogram or stem and leaf plot Check sheet Pareto chart Cause and effect diagrams Defect concentration diagram Scatter diagram (scatterplot) Control chart

Control Charts: The “Big Idea” Monitor process output If variability in process is just random sampling variability, values should be within control limits If other sources are present then values may be beyond control limits

Recall: Sources of variability Common Causes Random/chance variation Process is stable Assignable Causes Process shifts or becomes more varied Variability in process that comes from specific causes Can (and need to) be identified and removed

Cause and effect diagrams Identify assignable sources of variability Also called Ishikawa or “Fishbone” diagrams

Cause and effect diagrams Define the problem to be analyzed Create a group with knowledge of the process that can draw the diagram Diagram components: A horizontal arrow with the problem to be studied in a box on the right. Major branches with main causes. Additional arrows within each major branch with secondary causes. 

Cause and effect diagrams Result (i.e. the problem)

Cause and effect diagrams Major factor 2 Major factor 3 Major factor Result (i.e. the problem) Major factor 4 Major factor 5

Cause and effect diagrams Major factor 2 Major factor 3 Major factor Result (i.e. the problem) Sub- factor Sub- factor Sub- factor Sub- factor Sub- factor Sub- factor Major factor 4 Major factor 5

Example cause and effect diagram

Example cause and effect diagram Can’t be controlled

Questions for you

Pareto chart Bar chart of attribute data Arranged in frequency order Target most common problem for improvement Caution: Most common problem is not necessarily most important problem

Example Statistics exam 20 multiple choice questions Which topic missed most?

Example Pareto chart

Example Pareto chart

Pareto chart Bar chart of attribute data Arranged in frequency order Target most common problem for improvement Caution: Most common problem is not necessarily most important problem Solution: Create Pareto chart of cost or importance to accompany frequency chart

Histogram or Stem and leaf plot Explore distribution of a variable Histogram better for large datasets Stem and leaf (or dotplot) better for smaller datasets

Check Sheet Written checklist of defects By type, locations, or cause (e.g. machine, worker) Ordered by time to observe trends Could be used for data collection/entry to then create other charts E.g. control chart, Pareto chart

Example Check Sheet

Defect concentration diagram Picture of unit that shows all relevant views (e.g. front, back, sides, top, bottom) Shows location of defects May point to cause of defects Ex: Lever used to move unit on assembly line has a worn pad

Example defect concentration diagram

Example defect concentration diagram DE, SC DE

Scatterplot Explore relationship between two variables Between possible assignable cause and output Overall form of relationship Linear or not Direction of relationship Positive or negative Strength of relationship How tightly clustered together are the points?

Example scatterplots Strong, positive relationship No relationship Weaker, negative relationship