If you ever plan usability testing activities for a medical device, you may find yourself responsible for defining usability objectives. Today’s topic is - What makes a good usability objective?

Usability objectives (or requirements) are typically driven by either safety concerns or business goals. Safety related objectives should originate from the risk management process and are designed to show that risk mitigations are effective. Business related objectives usually come from market research – what the customers are looking for and what the competition currently offers.

The most effective usability objectives contain several key elements:

  • Task – including a quantitative goal so that success can be easily defined, usually in terms of time, accuracy, task completion rate, etc. The highest risk tasks and the most important tasks for using the device effectively should be included when defining tasks.
  • User profile – specific user group that will perform the task.
  • Use environment – context of device use for a particular task, including physical and social environmental factors. Use environment is not always specifically called out in the usability objective but is often implied. It should, at a minimum, be defined for the device in the usability documentation and considered when developing usability objectives.

As much as possible, objective (performance based) tests should be used to evaluate usability objectives, especially those related to the safety of the device. Subjective (often preference based) tests may also be used but are somewhat arbitrary and should be used in addition to, rather than in place of, performance tests whenever possible. Both forms of feedback can be valuable and should be considered when developing usability objectives.

Here are some examples of well-defined usability objectives. See if you can guess which ones are motivated by safety concerns or business goals, and whether they require performance testing or preference testing. (Answers are at the bottom of the post – No cheating!)

1. “90% of experienced* technicians shall be able to set up the system for use in a laboratory setting within 3 minutes.”

2. “80% of experienced* ICU nurses shall prefer the user interface of this infusion pump to that of their existing infusion pumps.”

3. “100% of trained** surgeons shall be able to correctly connect the device tubing to the patient cannula without visibly introducing air into the circuit.”

*Level of experience could be quantified by a knowledge test or by simply asking how many years of experience a user has.

**Training should be controlled and consistent across users.

You might think – Those usability objectives are nice, but where do those percentages come from? How do I define acceptance criteria for my objectives? – Check in next Wednesday to find out! In the meantime, if you define usability objectives differently let's talk about it!

-KB

1. Business, performance. 2. Business, preference. 3. Safety, performance.

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