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Poka-yoke (pronounced poh-kay yoh-kay) is Japanese for avoiding errors. It is a concept first promoted in the early 1960s by Shigeo Shingo(1) and later popularized by his 1986 book Zero Quality Control: Source Inspection and the Poka-Yoke System. Poka-yokes are inexpensive, simple methods built into processes that prevent defects by eliminating errors or alerting us when errors are made. The key trait of poka-yokes is that they make it impossible for the error to occur in the first place. For example, electric outlets and plugs are designed so that it’s impossible to insert them together in the wrong way. Though poka-yokes may appear to be most applicable to manufacturing, they’re used in all sorts of processes, products, and services.
Automatic shut-off mechanisms for irons and portable heaters
Car lights that automatically turn off the ignition is switched off
Sink faucets with sensors that automatically turn the water on and off
Automatic garage doors with sensors that stop the door from closing when they encounter an obstruction
Color-coded file folders
Electronic forms that validate city names to postal codes
User accounts that aren’t activated until a confirmation email is responded to
In-room self-checkout at hotels
Fast-busy when an analog telephone is left off the hook
Most of us think of quality tools only as a way of enhancing the customer experience through the elimination of defects. But if we creatively applying the poka-yoke technique, we can not only make inexpensive improvements to our products and processes by preventing errors, we can add value by making them friendlier for the consumer to use.
The Poka-Yoke Technique
1. Understand why people make mistakes.
2. Look for error-prone elements.
3. Look for poka-yoke fixes.
1. Understand why people make mistakes
If we don’t understand the human factors that can lead to mistakes, we won’t be able to develop effective poka-yokes. There are four factors that contribute to people making mistakes(2):
Attention: We can focus well only on a single activity at a time. Multi-tasking and interruptions will result in a greater likelihood for errors. And over time, with most experts suggesting in as little as 20 minutes, repetitive processes become automatic responses and we no longer pay conscious attention to what we’re doing.
Perception: People analyze a situation by interpreting sensual elements and synthesizing them into a rational response. This can lead us to misjudge a situation if all of the sensual elements don’t agree. For example, advertisements grab our attention with large text, pictures, and bright colors, but it’s often the extremely small, innocuous print at the bottom of the ad that’s most important for us to read, yet because of its comparative obscurity, our minds gloss over it as unimportant.
Memory: Short-term memory is good for small chunks of information for very brief periods of time, but it has to be moved to long-term memory to remain effective. So unfamiliar or new procedures are error-prone. There are also many factors, including stress, fatigue, boredom, and noise, that limit how well we can retrieve long-term information, which means regardless of how thorough our training might have been, it can be forgotten, and we make mistakes.
Logical reasoning: Panic, stress, and pressure can cause even an experienced worker to jump to the wrong conclusion. For example, many infamous industrial accidents escalated because the operators thought the gauges were at fault, giving them inaccurate information, rather than deducing that there was indeed a critical flaw in the process.
2. Look for error-prone elements
At its most basic level, poka-yoke requires only a questioning approach as we look at a product or process. We can start by looking for the tell-tale signs that a process is a candidate for poka-yokes that are easy wins:
It has repetitive elements and repeatable outcomes.
It requires specialized skills or training to perform.
It requires attention to detail.
The people performing the task are apt to get frequently interrupted.
The process has frequent delays, such as when one of the process participants is waiting on somebody else for further action.
People in the process are multi-tasking.
Another method of analyzing a process is to ask ourselves the 5W’s about it. We can then review our answers to identify weaknesses in the processes:
Who: Who are the participants? What roles participate in the process? What are the skills of roles involved? How familiar are the people with the process?
What: What kinds of errors or defects are likely to be introduced during the process? What kinds of steps are repetitive in the process? What errors can be introduced by another process?
When: In what stages are errors likely to be introduced? In what stages are errors that were introduced earlier in the process likely to become apparent?
Where: Where or through what mechanisms are errors or defects introduced (such as tools, machinery, applications, or devices)? Where do interruptions occur in the process? Where are there long delays in the process? Where are there hand-offs from one person to another?
Why: Why would errors or defects occur? What conditions can lead to errors being made? What process components can lead to errors? What human elements can introduce errors or overlook a defect condition?
If we’re analyzing a service-based process, we also have to consider the failures that might be introduced by the customers(3):
Failure to understand their roles in the process;
Failure to engage the correct service;
Failure to set expectations;
Failure to follow the process in the correct order;
Failure to follow instructions;
Failure to alert us of service failures;
Failure to adjust expectations;
Failure to perform their necessary post-process actions.
3. Look for Poka-Yoke Fixes
With potential failures identified, we can now look for solutions. Poka-yoke fixes don’t rely on training to prevent errors or detailed human inspection to identify defects because those methods require the participants to think about what they are doing 100% of the time, and that is itself a point of failure.
As we consider solutions, it’s easy to get carried away with complexities. If our solution is overly convoluted, costly, or requires a form of inspection afterward to identify the defect, it probably isn’t a poka-yoke. The key characteristics of successful poka-yokes are that they: are simple approaches; are inexpensive (which is why they’re best incorporated during design phases); are built into the processes; provide immediate feedback to the people in the processes; and take no thought from the participants to invoke.
There are two primary types of poka-yokes. The first is a shut-out type of approach where we make it impossible for the error to happen, and the second is an attention-type of approach that provides a distinctive warning when an error condition exists. As an example, let’s consider an online shopping cart application that asks the consumer for his or her desired delivery date and shipper preference from one of two shippers.
The first shipper doesn’t deliver on a Saturday or Sunday, so if the consumer chooses that shipper and a Saturday delivery date, the order is not submitted and a warning is displayed, asking the consumer to choose a non-weekend date or change his or her shipping preference. This is a shut-out mechanism because the process halts and isn’t allowed to continue when the error occurs.
The second shipper will deliver on Saturdays for an additional charge, so in this situation a prompt is shown that explains what the extra delivery charge will be and gives the consumer the choice of accepting the charge or going back and changing the order’s shipper. This is an attention-type or warning mechanism because it doesn’t definitively prevent all errors (the consumer may not read the prompt and still later dispute the additional shipping charge).
Using Poka-Yoke Concepts for Innovative Improvements
Many people would not consider poka-yokes as innovative. Poka-yokes are usually part of quality and continual improvement efforts, such as Kaizen, and there is a lot of controversy as to whether incremental or small-scale improvements are innovation or not. But limiting what we think of as innovation immediately puts a collar around creativity and constrains our viewpoint before we’ve even started. Innovation can start from the smallest effort and idea, and if we approach poka-yokes with a broader viewpoint and in combination with solid process design, analysis, and improvement techniques, they can have innovative consequences. The product or project team can use the poka-yoke technique not only to make defective-free products, deliverables, and services, but also to add low-cost but high-value attributes that improve the customer’s experience.
To find poka-yokes of this type, we have to get beyond our intimate knowledge about the product or process we’re analyzing and look at it from the customer’s perspective. Because of our familiarity with it, we’ll have a tendency to keep our focus narrow. For example, if we’re in the human resources department and we’re analyzing our new hire process, we’re likely only focusing on HR-centric processes, and we may not think to look for poka-yoke opportunities in related processes owned or controlled by other departments. But from the perspective of the newly hired employee, it’s all one experience, and a failure is a defect regardless of whose ultimate responsibility it was for preventing the error.
When we look at a product or process from the customer’s viewpoint, we can better anticipate failures in a much wider context, and preventing those defects directly enhance the customer’s experience.
When the customer comes in contact with the product or process, what are his or her expectations about it? Which of those expectations might not be met? Which defects are in our direct control to fix and which could be caused by other processes? What negative customer experiences might occur but which are only indirectly involve our product?
In ways beyond the intended use, how might the customer use the process or product? Is there market value in those uses, and if so, how can we incorporate low-cost mechanisms that promote rather than impede that multi-functionality?
What types of failures can occur when used as intended or in the case of a process, followed per instructions? What types of failures can occur when the product or process isn’t used as intended?
Last, without introducing unnecessary quality and costs, what poka-yoke mechanisms can we introduce that improve the customer’s experience?
For examples of customer-oriented poka-yokes, please see the full article.
Poka-yokes are simple but effective quality assurance methods that prevent errors. To apply the poka-yoke concept, we need to understand why people make errors and we have to analyze the process to know where errors are likely to occur and what root causes contribute to them. But by taking a broader viewpoint of failures, we can use poka-yoke techniques during the design phases of products and services to find where we can incorporate low-cost features that improve the customer’s experience.
Copyright 2010, J. Alex Sherrer, Project Management Road Trip
1. Wikipedia. (n.d.). Poka-Yoke. Retrieved from http://en.wikipedia.org/wiki/Poka-yoke
2. Parliamentary Office of Science and Technology, United Kingdom. (June, 2001). Managing Human Error. POSTnote, June 2001, (number 156). Retrieved from http://www.parliament.uk/post/pn156.pdf
3: Chase, R. B. and Stewart, D. M. “Make Your Service Fail-safe.” Sloan Management Review, Spring 1994 (Volume 35, Number 3), 35.