Success rates tell you whether people managed a task. Two short, standard questionnaires add how it felt: the Single Ease Question (SEQ) after each task, and the System Usability Scale (SUS) at the end of a study. Because both are widely used, you can compare your scores with published benchmarks.
The Single Ease Question (SEQ)
One question, asked straight after a task:
Overall, how easy or difficult was this task?
People answer from 1 (very difficult) to 7 (very easy).
What's a good score? Across many studies, the average task scores about 5.5. Treat anything below about 4.5 as a task people found hard, and anything around 6 or above as easy.
Why use it? It's quick, so it doesn't slow the study down, and it catches problems success rates miss. A task people completed but rated 3 out of 7 deserves attention.
Tip: ask a follow-up only to people who rate the task 3 or lower, such as "What made it difficult?". You get the reason without asking everyone an extra question.
The System Usability Scale (SUS)
Ten statements, asked once at the end, each rated from 1 (strongly disagree) to 5 (strongly agree). They alternate between positive and negative, for example:
- I thought the website was easy to use.
- I found the website unnecessarily complex.
How it's scored: for the odd-numbered (positive) statements, subtract 1 from the answer. For the even-numbered (negative) statements, subtract the answer from 5. Add the ten results and multiply by 2.5. That gives a score from 0 to 100.
It's not a percentage, even though it runs to 100.
What's a good score? The average across published studies is about 68.
| Score | Roughly |
|---|---|
| 80 and above | Excellent |
| 68 to 80 | Good, above average |
| 51 to 68 | Below average |
| Below 51 | Poor |
Why use it? It's reliable even with modest sample sizes, it's been used for decades, and a single number is easy to track over time and compare between versions.
Tip: keep the standard wording. Changing the statements makes your score harder to compare with benchmarks. Replacing "system" with "website" is a common, accepted adjustment.
Which should you use?
- SEQ when you want to know which tasks felt hardest. Use it in tree tests and first-click tests, after each task.
- SUS when you want one overall usability score to track over time. It's best for something people have used for a while, such as a whole site or prototype, rather than a single screen.
- Both in a study where you want per-task detail and an overall score.
In ClickTree you can add the SEQ to any tree or first-click task, and the SUS at the end of any study. Both are scored for you, and the results show where you sit against the benchmarks.
Want to add follow-up questions? See how to write good tree test tasks.