If you have been confirmed by your colleagues as a bona-fide member of teaching staff in your school, you can now see a list of all the questions in a quiz, together with the global response statistics for each question, before you assign it.
Why only for confirmed members of staff? It’s just an anti-cheating precaution.
After launching this, I found a couple of issues that were tripping people up.
Quizzes you authored yourself
If you own a particular quiz, you will continue to see the EDIT button rather than the STATS button. The Edit page is actually a Statistics page, with additional authoring features.
Questions listed by topic
The Stats view is not available from the topic lists. Search for the quiz you want in the Resources page instead.
Show all vs. collate by tag
You can view statistics in two ways. “Show all” is self-explanatory, and is the one you are most likely to want for previewing questions. “Collate by tag” groups questions according to the Key Concept tags so that you can review the overall level(s) of understanding of the students. The value you select is remembered and applied by default to the next stats page you look at.