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  • Aaron Wolfson thinks this is interesting:

A clickable prototype can be as simple as hooking up a few wireframes together so that when users click on a button they move to another static mockup. It can be as complicated as building a whole user interface that behaves almost identically to what a user would see in a real product but doesn’t do anything on the backend. The closer you can get to the end product, the better the feedback you’ll get.

From

Cover of UX for Lean Startups

Note

It's a trade-off between time/money spent and quality of feedback.