Appendix 5: Commentary on the Difference Between “Usability” and “Accessibility” May Be the End Users

The distinction between the terms “usable” and “accessible” may be no more than the identification and definition of who the end user is: if a device is usable by someone who has a disability, then it becomes labeled accessible. The two terms lie on a continuum of design accommodation.

Figure 1. Relationship between mainstream design, assistive technologies, and expert systems.

Figure 1 shows a relationship between mainstream design, assistive technology, and expert systems. Most people in the population have abilities that lie in the middle portion of the normal distribution curve and mainstream design suits them fine. But either in place of or in conjunction with mainstream designs, people whose abilities fall on the lower end of the curve may benefit from use of assistive technologies, and people whose abilities fall on the upper end of the curve may benefit from use of expert systems. Note the large “gray zones” between the categories, where some mainstream designs may not extend (in fact, there may be a gap between categories), or depending on context and perspective, a device may be considered to fall into either one.

Small changes in design of a mainstream device can have a large effect on usability and accessibility. We will always need assistive technologies because no design will ever be usable by all people in all circumstances; and beyond the extent of or along with assistive technologies, we will always need personal assistance. But making a device be more accommodating of a broader diversity of user abilities also makes it suit a variety of user preferences (e.g., learning or operational mode) and circumstances (e.g., dark hallway, noisy emergency department or occupied hands), and may reduce the need for assistive technologies (and/or expert systems).

The concepts of usability and accessibility are not mutually exclusive; and while difficult to achieve, in the interest of improving the interactions between people and medical devices in order to increase healthcare access and safety, progress toward both goals should be accepted as a beneficial design challenge, not condemned as an unnecessary burden.