Quality Progress - January 2016 - (Page 27)

Best of BACK TO BASICS That's So Random-or Is It? A ssignable cause, random variation, process stability, process capability-these terms can easily confuse those new to process management. Does random variation in a process automatically require process improvement? Can a process be stable and capable with an assignable cause present? Not knowing the answers to questions like these can cause process owners to overengineer and possibly overcorrect their processes. A simple example of random variation is the process of driving to work. Let's say your typical drive time is 20 minutes, but it's not exactly 20 minutes every day. There are random variables or causes that impact your drive time, including the speed at which you drive, traffic patterns and the time you leave the house. So the random process variation may extend from 18 to 25 minutes. One day, however, your drive time increases to 55 minutes (see Figure 1). You investigate the cause and determine there was an accident, which caused the process to spike out of control. The accident is the assignable cause of the out-of-control situation. In other words, you know what happened and can assign a cause to the out-of-control situation in the process. Even though you know what caused the increase in drive time, you wouldn't revise the process because of this one assignable cause. The same theory applies to business process management. You need to Identify and investigate all assignable cause incidents. establish a random process variance for each of the processes for which you're responsible, such as the drive time variance of 18 to 25 minutes. You need to know what you can expect and plan for every day. Then, when random, assignable cause incidents that negatively impact the process occur, you need to investigate the cause, assign a cause, document the cause and continue to monitor process performance. An assignable cause log (see Figure 2) can effectively document assignable cause incidents, allowing you to capture the information for use in process performance reviews or improvement projects. If an assignable FIGURE 1 Drive Time cause incident becomes chronic 60 50 or recurring, you Assignable cause 40 will need to 30 20 apply a process 10 improvement to 0 Mon. Tues. Wed. Thurs. Fri. Mon. Tues. Wed. Thurs. Fri. bring the process Drive time back into control or to the previous acceptable level of process variaFIGURE 2 Assignable Cause Log tion. To illustrate this point, let's Control plan measure: drive time say your drive time increased to Assignable 55 minutes per Date cause detail Action taken Date day for five days 5/23/05 Drive time Investigation revealed an isolated 5/23/05 in a row, causing increased to incident-an accident occurred. you to be late for 55 minutes No improvement needed at this time. work all week, 96 I MARCH 2006 I www.asq.org MARC 2006 H by Cecelia McCain which is unacceptable. Now you have a chronic, recurring, out-of-control situation, so you need to investigate the cause and implement a process improvement. After investigating the cause, you determine the train schedule changed, which negatively impacted the flow of traffic. Therefore, you need to adjust or improve the process to remove the now chronic assignable cause. Simple improvements include changing your driving route or work schedule or leaving home earlier or later to mitigate the negative impact of the changed train schedule on your driving time. More complex and drastic improvements include selling your home or changing jobs. Random cause variation is inherent in every process, from simple order taking to complex automobile assembly. Look at the processes in your own organization and identify the extent to which random variation exists by plotting the data over time. Use simple control charts and establish upper and lower control limits to maintain a stable process. Assignable cause will occur in every process sooner or later. The key to effective process management and stability is to investigate and identify all assignable cause incidents, while remembering you don't need to make process improvements after every occurrence. CECELIA MCCAIN is the director of quality program management at Compuware Corp. in Detroit. She is a member of ASQ and a certified Six Sigma Black Belt. Please comment If you would like to comment on this article, please post your remarks on the Quality Progress Discussion Board at www.asq.org, or e-mail them to editor@asq.org. January 2016 * QP 27 http://www.asq.org

Table of Contents for the Digital Edition of Quality Progress - January 2016

According to Plan
Solid Proof
Use Your Head
Stakeholder Management 101
Customer Delight
All About Data
Eight Simple Steps
Minimizing Chaos
Take Note
Pyramid Scheme
Assessing Failure
Which Six Sigma Metric Should I Use?
Turning ‘Who’ Into ‘How’
In the Beginning
Outputs and Outcomes
That’s So Random—Or Is It?
Understanding Variation
Improving a System
Putting It All on the Table
Know the Drill
It’s Fun To Work With an F-M-E-A
Solve Problems With Open Communication
Tell Me About It
Separate the Vital Few From the Trivial Many
To DMAIC or Not to DMAIC?
Breaking It Down
Smart Charting
1 + 1 = Zero Defects
QFD Explained
Curve Your Enthusiasm
Make a Choice
What Is a Fault Tree Analysis?
Successful Relationship Diagrams
The Benefits of PDCA
Creative Combination
Return on Investment
The Art of Root Cause Analysis
Why Ask Why?
Get to the Root of It
Checks and Balances
Calculated Risk
Sufficient Evidence
Sample Wise
Clearing SPC Hurdles
Supplier Selection and Maintenance
Team Advantage
Building a Quality Team
Plan Experiments to Prevent Problems
Substantiation Test
Training Day

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