I'd argue that usability also must include accessibility and I highly doubt that in your 15 user sample set you will cover the deaf, the (color) blind, the dyslexic, the paralyzed, the epileptic and various other groups of people with special accessibility requirements.
Or, for an American developer, what are the odds that your 15-user sample will find usability problems having to do with your icons only making sense to someone in the US? There's more to localization than just translation. Or if you have a product that does voice recognition, what range of accents are you covering with those 15 users?
That's OK, we nowadays use icons that don't make sense to anyone at all. I mean how would you know that three horizontal lines was a "Hamburger menu", and if you do know that, why would you want a Hamburger?
Actually the icon looks like three menu items. It is a pretty good icon for signaling that it will open a menu. The hamburger nomenclature seems to be an ex pos facto name for something that rightfully should be called the menu icon.
It's a nondescript icon made of three horizontal bars, it looks like literally anything that comes in threes. My mom calls it the pancake button and my fourteen year-old nephew used to call it the button with something that looks like a fork but without a handle until he switched to the "meh" button once he became a nihilist (teenagers do that stuff sometimes). A menu with three items is very likely to be among the last things that crosses a non-techie's mind.
At this point it's been used enough that anyone with enough exposure to electronics knows what it does, but it's hardly a better choice than the "File" menu. The point of making something intuitive, as opposed to explicit (i.e. by using a symbol as opposed to spelling out) is kindda missed if you need to "well actually" it and explain why it means whatever it means.
I disagree. It took around two years of seeing hamburger menus before it clicked that it was a common symbol for a menu. Its getting worse and seems to be getting replaced by 3 vertical dots now.
I can only speak for myself, but for me who grew up with C64, Windows 3.1, 95, 98, Linux, Windows XP more Linux etc that icon still didn't make sense until I got it explained.
Then again, the magnifykng glass icon for search didn't make sense either until I read the docs but at least back then people made docs and kept the UI stable enough so that it made sense to learn it.
I still remember fondly being good with OLE (Object Linking and Embedding) in a Microsoft Works.
No I think that having a bit of descriptive text below an icon was far more useful than far prettier world of nicely rounded corners on hamburger menus that we have today.
Usability should include accessibility when possible, but there is no must here. There are lots of tools that need usability testing that have a sufficiently small team and user-base to make accessibility a waste of time and resources.
Indeed, on teams and products of any size there is always a decision to be made about which accessibility requirements will be met and to what degree.
I would make the separate argument that what you need with accessibility requirements is separate testing expirements for each one. You don't need 100 testers to to make sure you have some special accessibility requirements, e.g. you need 15 normal vision testers and 15 impared vision testers.
