Guidelines for Good Design

Medical We are asked by clients to review their existing products or designs to make recommendations on improving usability (see our Usability Bench Test). Time-and-time-again, we find that the most common design problems cHere are three of our favorite our top five guidelines for good design.

Provide Unambiguous and Timely Feedback

From our experience, this is the most pervasive problems for user interfaces, including those for medical devices. Providing clear and timely feedback to users on the state of a system or the outcome of an action is critical for learning, use, and minimizing use-related errors.

Unambiguous and timely feedback is also key to minimizing use-related errors.

Make Things Visible

A well-designed device interface conveys information to the user about the devices function, operational modes, and controlling actions. If a design

how interface is organized; workspaces

how to navigate vertically or horizontally within the structure

includes navigation scheme.

nurses goal is to set alarm limits, but instead she gets lost in a confusing hierachy of setup options and screens.

labeling screens with header
adhering to strict navigation model (e.g., same "forward," "backward," "ok," and "go to main menu" choices always presented in same location)

Make the Display Flow Match the Task Flow

Western convention is for viewers to acquire information on a page or display by scanning left to right and top to bottom. Screen layouts should be designed with this in mind. In particular, when the screen supports a commonly performed task, the spatial organization of controls should mirror the sequence of steps required to complete the task.

Here is a simple test of whether the screen flow matches the task flow: on a printout of a screen, use arrows to draw the sequence of interactions with information or controls required to complete the task. The "task signature" should look something like it does in A. If it looks like B, the screen flow doesn't support the task flow.

"Task Signatures"

Prioritize, Prioritize, Prioritize

One difficulty companies often have is managing the complexity of their medical software applications. Typically, complexity comes from the ever expanding product feature sets, as new versions of the software "add-value" by adding more features. New features are added to the appropriate menus, windows, and dialogs as additional data points and user interface controls. The end result is too often visually cluttered, dense displays with a myriad of commands and options.

Overly dense displays can be intimidating to nurses, technicians, physicians, and patients. Screen density also makes it difficult for new or casual users to identify the data points and UI controls needed to complete routine, high-frequency tasks. Moreover, screen density will slow down performance of experienced users. Using smaller, more tightly packed controls makes people slower at selecting any one of them, an effect immortalized by Paul Fitts in 1954 as Fitts' Law.

Good designs adopt a "task frequency" approach to prioritizing and organizing product features and functions. Main screens should present only those data points and UI controls needed to perform routine (or otherwise important) tasks; everything else should be relegated to secondary and tertiary screens and popup dialogs.