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What does it actually mean to say a product is usable?

In this episode of The Design Psychologist, Thomas Watkins talks with Phil Kortum about the System Usability Scale, or SUS: one of the most widely used tools for measuring usability. They discuss why this 10-item questionnaire has lasted for decades, what makes a usability metric trustworthy, and how researchers can use SUS scores to compare products, track improvement, and communicate usability in a shared language.

The conversation covers why a number is not automatically objective, how SUS differs from measures like Net Promoter Score, when the positive version of SUS may be better to use, and why usability researchers still need effectiveness and efficiency measures alongside subjective ratings.

They also explore Phil’s work on voting systems, where usability is not just about convenience but whether people can successfully cast a vote.

If you want to understand how to measure human experience with more rigor, this episode gives you a clearer way to think about usability, evidence, and the difference between a score that sounds scientific and a metric you can actually trust.

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