Poka-yoke
Poka yoke, pronounced “POH-kah YOH-keh” — is a Japanese term that translates as “mistake-proofing” (from the Japanese yokeru (avoiding) and poka (inadvertent errors). A poka-yoke device is any mechanism that either prevents a mistake from being made or makes the mistake obvious at a glance. The idea is to prevent errors from being made in the first place, or if they are made, making those errors very obvious. The concept was formalised on the Toyota production lines by the Japanese industrial engineer Shigeo Shingo.
Mistake proofing
Shigeo Shingo defines three types of Poka-Yoke:
- The contact method identifies defects by whether or not contact is established between the device and the product. Color detection and other product property techniques are considered extensions of this.
- The fixed-value method determines whether a given number of movements have been made.
- The motion-step method determines whether the prescribed steps or motions of the process have been followed.
A familiar example of the poka-yoke philosophy is the 3.5″ floppy disk. You probably won’t need reminding that the top-right corner is shaped in a certain way, meaning the disk cannot be inserted upside-down. Undoubtably helpful in all sorts of situations, so how can this be applied to the web and websites?
Certainly one the most frustrating objects encountered on many websites is the ubiquitous web form. Where ever you go on the web, a form is the most likely way you are going to interact, order, sign-up, comment or log in. There are server-farms full of pages on how to create html forms so I’m not going to go into code detail, but maybe it’ll be instructive to run through Shingo’s three types of poke yoka with respect to internet forms.
Our goal is to remove, or at least reduce, the number of errors occuring on our forms. Often sales or contacts are lost when users become frustrated by malfunctioning online forms. The more we can do to prevent mistakes in the first place, the less money we’ll spend fixing things later, and the happier our customers will be!
The 1-10-100 Rule states that as a product moves through the production system, the cost of correcting an error multiplies by ten. Ensuring an order is correctly entered costs us £1. Detecting an error at the billing stage costs £10. If the error isn’t caught in time and is passed on to the customer, that costs us £100 to fix. If we don’t fix it at that point and the customer complains to their friends, the cost can quickly escalate to £1000!
The Contact Method
This group of checks include “methods in which sensing devices detect abnormalities in product shape or dimension by whether or not contact is made” (Shingo). These methods are usually used to check size, shape, orientation, presence/absence, or appearance. They are also referred to as “physical poka-yokes”.
Although web forms don’t usually handle product shapes and physical objects, I think in this group we can include the following tests:
- always make sure an email address is correctly formatted (often acheived by testing the ’shape’ of the address, in that it contains an at symbol and a fullstop)
- required fields must always be tested for the presence of a valid string
- phone number fields must contain numbers
The Fixed-Value Method
Fixed-value methods – or counting poka yokes – determine that a fixed number of movements have been made and is analagous to ensuring all your required fields have been completed. But they might also be seen in online games, or where users have to accept terms and conditions. A purchase-step progress bar could also fit into this category – those identifiers that graphically display your progress in an online transaction. They give you a count of how many pages you are away from completing your transaction, thereby providing some reassurance that progress is being made.
The Motion-Step Method
The third poka yoke method uses sensors to determine if a motion or step in a process has been completed. If the step has not been completed or has been completed out of sequence, a sensor signals the process should stop.
When applied to the web, you can quickly see who this can easily be enforced by a suitable linking strategy. Users should only be presented with links that are relevant to their current situation. And if they are about to make a purchase, don’t complicate matters with adverts that can distract and lead them astray.
If an email address has been entered incorrectly, ensure the user is made aware of that fact immediately, rather than when they submit the form.
Summary and comments
The concept of a poka yoke device is useful in reducing errors made by users. Reducing the occurence of errors leads to lower costs and happier customers. Poka yoke is well established in the industrial work place, applying the concepts to web pages isn’t a perfect fit but the essential principles can help establish good working practices that lead to improved user experiences.
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