> "In God we trust, all others must bring data." Best practices should be grounded in data rather than opinions whenever possible, especially when they're based on claims about users' cognitive load like in the NN/g recommendations.

Indeed they should. Except that here, the case is bloody obvious. "Show me the data that says the grass is green!" "Show me that evolution exists!" The onus of finding the data is on whoever thinks the statements are unreasonable.

Look… Opening links in new tabs does break the back button; no extra evidence is needed here beyond stating the obvious. The hardware back button on Android phones do lead to unexpected behavior; no extra evidence needed either. Having a save button in a word processor is needlessly forcing 40-year old IO limits onto end-users; no extra evidence needed here either.

In each case, what you can argue with and request data for, is this: whether end-users successfully cope with it or not; not whether it's broken to begin with.

And sadly, we humans are wonderfully adaptable. Including to pathetically poor user interfaces decisions such as the need to click a Start button in order to shut down a Win95 computer.

> Besides, mobile browsers have gotten a lot better at managing RAM and most have been able to optimize background tabs for a long time, so I think the RAM issue is way overrated.

Not everyone has a modern device. A whole bunch of iOS 5.1 devices (3rd-gen iPhones, 1st-gen iPads) and old Android devices are still in the wild.

> For example, many people expect "help" links (like the one next to the HN comment box) to not make you leave the page and rely on the "back" function to restore your painfully typed comment once you realize it does.

And that would qualify as a session that shouldn't be interrupted — i.e. it's a perfectly valid use-case, including for the OP.

(I, for one, would nonetheless suggest that a floating div on the same screen might be superior in that case, because the current window/tab would not lose its focus — a hopefully obvious fact.)

> a lot of things break the back button because dynamic content has made it much easier to do so

Assuredly so. But two wrongs don't make a right, so posting that as a reason to break it further is dubious at best.

Speaking personally, I hate those sites because they break my back button. I actually use the damned thing a lot, come to think of it. Especially on my 1st-gen iPad, since RAM-starved device can't seem hold more than a tab or two in memory when browsing sites loaded with JS.

> the point of doing an actual study is to be able to measure them so we can compare them and say which trade-offs are worth it and which aren't

Indeed. But chances are you wouldn't actually be measuring these things due to the huge bias involved in the measurement itself.

By simply asking a user if he prefers A or B, even qualitatively, you may open up a whole new world that he was unaware of until you asked; if so, the odds are good that — of course! — he'll prefer it rather than his more familiar daily routine, since the latter is in shambles due to widespread bad practices.

But hold… Your profile states that you're a data scientist, and I see you attended IEP at that. So you necessarily know this, and the — obvious — fact that a great many studies out there are inconclusive due to dubious methodology.