The Limits and Interpretation Pitfalls of Fitts’ Law

I’m getting old, and there are things that I don’t notice too well anymore. But I’m pretty sure UI elements have been getting bigger. Everywhere.

That makes a lot of sense on touch devices. Fingers are big and bulky, and the widgets that press them need to be big and bulky. But why are UI elements getting bigger everywhere, even on devices that aren’t touch-enabled, or for applications that are nowhere near being productively used on touch-enabled devices, like IDEs?

There is a reason that everyone is citing ad nauseam these days: Fitts’ law. It’s “popular” formulation states that bigger widgets are easier to hit, and the obvious interpretation is that we need to make them bigger. The reason why you can fit about as much code on your 24″ Full HD monitor as you could fit on the old Trinitron you had back you saw The Matrix at the cinema is SCIENCE!

I want to argue that:

  1. This is an incomplete and narrow interpretation of Fitts’ law, and
  2. That this is an unproductive use of Fitts’ law, because
    2a) It is routinely applied without any numerical analysis, and
    2b) It fails to account for other metrics, and consequently it rarely results in good design trade-offs

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