The Poka-Yoke principle in UX design
The art of preventing errors
Origins
The Poka-Yoke principle was originally applied by Toyota’s industrial engineer, Shigeo Shingo. The term “poka-yoke” means “error-proofing”, the main goal is to minimize the likelihood of human errors in the process.
Examples from the world around us
- USB stick with a specific orientation
- Medicine bottle with childproof opening
- Automatic turn-off on home appliances
- Microwave oven that stops running if you open the door
Case study: Chrysler’s gear design
In 2016, Chrysler recalled 1M+ of their cars due to a problematic gear shifter. The problem was that after shifting, it returned to its central position, so there was no positional feedback (only lights), so drivers had to look. In many cases, drivers thought that the car is in park, go out of the car, then the car drived off. This caused several injuries and accidents.
“Gear-selection is conveyed to the driver by multiple sets of indicator lights, not gear-selector position, and unless due care is taken, drivers may draw erroneous conclusions about the status of their vehicles.” (Source: cnet.com)
So basically according to Chrysler, it is not their fault, it’s a “driver error”.
Check out my sketch about mental models.
How to apply this principle
You, as a designer should ask:
- What can go wrong?
- What are the existing mental models?
- What are the risks?
- What are the worst case scenarios?
Create journey maps / user story maps, then add potential risks, errors to each steps. Then ask: how can these be prevented?
The key takeaway is that in many cases, it is not a user error, it is bad design.
Poka-Yoke in UX design: some examples
Some examples in digital product design:
- Provide meaningful and timely feedback to the users
- Add confirmation dialogs
- Apply additional deliberate friction e.g. at high-consequence steps (e.g. account deletion)
- Add autosave, revision history, undo and redo
- Form design, e.g.: validation, input constraints
- Password requirements, strength indicators
- Suggestions, e.g. Gmail’s forgotten attachment reminder
- However, instead of using disabled controls, in many cases it is better to enable & give feedback
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Recommended reading and useful links
I heard about Chrysler’s gear shifter in this awesome video by Jamal Nichols.
