Work With Us

How Affordance Makes Medical Devices Safer

(This post is based on the video, “Affordance” in the Design Defined: Design Principles Explained series.)

Have you ever tried to pull open a door, only to look down and see a sign that says “push”? If you have, you’ve encountered a “Norman door” and an example of poor design.

Named after Don Norman, the famous advocate for user-centered design and the author of The Design of Everyday Things, a Norman door signals you to do the opposite of what you’re supposed to do. At best Norman doors are a nuisance; at worst, they’re dangerous.

Norman Doors and Affordance

There’s a silver lining: Because we’ve all encountered one, Norman doors are the perfect example of poor affordance.

Affordance is the relationship between what something looks like and how it’s used. The user should be able to figure out how to use something just by looking at it.

Bars on doors are for pushing. Handles on doors are for pulling. (Knobs afford turning, light switches afford flipping, and steering wheels afford turning. … ) This is affordance.

Products Shouldn’t Require Signage

Norman doors have poor affordance, and because of this, it’s often necessary to add a “push” or “pull” sign to the door to correct users’ assumptions.

If a door is well-designed, it won’t need a picture, label, or instructions.

As Don Norman puts it, “Good design requires, among other things, good communication of the purpose, structure, and operation of the device to the people who use it.”

Affordance in Medical Product Design

In my own work as a human factors engineer, I think a lot about affordance as it applies to medical product design. In healthcare the stakes are higher than the momentary frustration caused by a Norman door.

If an auto-injector has poor affordance and its design makes it unclear to a user how to inject themselves, the user could suffer from a needlestick injury. If it’s unclear to nurses how to stop an infusion pump from delivering medication, it could cause harm to the patient.

Enhancing Affordance with Signifiers

To reduce the risk of user error, we sometimes add signifiers. These are cues that help a user understand how to interact with an object or device. Signifiers are used to optimize affordance, making it crystal clear how an object should be used.

On an auto-injector, we might add a ridge at the top to indicate where the user’s thumb goes, an arrow on a cap that shows you how to remove it, or a window in the shaft to see how much medication you’ve injected.

Observing Affordance Through Usability Studies

Researchers like me discover these potential use errors during usability testing. We watch participants try to use the product and encourage them to act just as they would in real life.

If they struggle, we let them struggle a little bit before we, as moderators, jump in and try to move them along and direct them. And while they’re struggling, we notice a lot of things we might never have known about without usability testing. User errors happen because there’s usually more than one way to accomplish a task. The correct way needs to be made obvious by the product’s design.

The designers and engineers on our project teams are often surprised by the insights that come from these formative evaluations.

Affordance Should Be Foundational

It’s important to do this research early so designers can build affordance and signifiers into their products.

The later you are in the design process, the harder it becomes to make a change — and the more likely you are to end up with a “push/pull” sign. It’s been proven that few people read instructions. And the FDA looks down on people changing their training or instructions, because it creates more risk.

That sentiment is clear in this excerpt from the FDA’s “Applying Human Factors and Usability Engineering to Medical Devices” (February 3, 2016):

“Design modifications to the device and its user interface are generally the most effective means for eliminating or reducing use-related hazards. If design modifications are not possible or not practical, it might be possible to implement protective measures, such as reducing the risk of running out of battery power by adding a “low battery” alert to the device or using batteries with a longer charge life. Device labeling (including the instructions for use) and training, if designed adequately, can support users to use devices more safely and effectively and are important HFE/UE strategies to address device use hazards. These strategies are not the most preferred, though, because they rely on the user to remember or refer back to the information, labeling might be unavailable during use, and knowledge gained through training can decay over time.”

By catching affordance challenges early in the design process, you’ll be able to address them in the device’s design to best reduce risk and prevent user errors.

Affordance in Digital Interfaces

Affordance is just as important in digital design as it is in physical design. (A link affords clicking, a slider affords sliding, and a magnifying glass icon affords searching.)

While filling out a form online, you know a field is required if there’s an asterisk nearby — and you know you’ve missed a required field if you’re not able to move to the next step. While testing the digital aspect of medical devices, we’ve caught user errors and built affordances into the next iteration of the software.

Icons can also create metaphorical affordance. For instance, a shopping cart indicates online purchases, and a floppy disc indicates the save feature. These icons are so ubiquitous and universally familiar that they don’t require additional labels or signifiers.

Applying Affordance to Your Device

Think about the products you design. How have you built affordances into them? How could you build affordances into them?

If users of a product you’re designing are struggling to execute an interaction or function, how can you modify the design to clarify the intended action?

Download our Design Defined ebooks to learn about more product design principles.