Usability and Accessibility – are they the same thing?

The more I study UI Consistency and improving the user experience, and the more feedback I hear from customers who use accessibility features, I’m really starting to wonder if Usability and Accessibility are really just two sides of the same coin?

Yes, there is a difference between the two.

  • Usability – how well a user understands the UI
  • Accessibility – the ability to use the UI

Is it possible to have one without the other?  Is it possible to have good usability without good accessibiltiy?  Is it possible to have good accessibility without good usability?  Let’s say that i have perfect MSAA support for a feature that works perfectly with Assistive Technologies.  Is it possible to have good usability without having good accesibility?

I don’t know yet.

I’m leaning towards “no, you can’t have one without the other because they are the same thing.”  During one of my 28 hours worth of meetings this week, I mentioned that if i went to graduate school for CS, i would probably write my thesis on this topic.

What do you think?

Comments (1)

  1. Will Pearson (MVP) says:

    Sara, Aaron, et al.

    This is something that’s been discussed on Scott Luebking’s UVIP group on YahooGroups. I fondly remember the discourse Chris Hofstader (of Freedom Scientific), myself and others had on this topic.

    We determined, and this is from the view point of end users and developers of AT, that you can have accessibility without usability. To explain a bit further, these are the definitions for the two terms that we came up with.

    Accessibility: whether someone can gain access to something, perform an interaction or operation, basically whether they can do something.

    Usability: Effectively, how well they can do it. Looking at measures such as efficiency, effectiveness, ease of use, accuracy, and user satisfaction.

    These are two terms that can be applied to anyone, doing anything, and they’re pretty universally adopted within the HCI community. They’re both attributes of an interaction or activity, so they will both be present, and can be measured through impirical testing.

    However, you can have something that is highly accessible, but not very usable. Say you had a dialog with 100 check boxes in it. Each were in the tab sequence, and so were reachable through keyboard navigation, each contained MSAA for AccName, AccRole and AccState, so people knew what they were. Thus, it’s the most accessible it can be, but if you wanted to change the value for check box number 50, you’d have to use a lot of keystrokes to get there, and listen to a lot of information, which you’d have to process, in order to determine if the check box you were on was the one you wanted. The GOMS model would look something like:

    Goal: Change state of check box for red

    repeat 50 times

    listen to check box name

    press tab

    end repeat

    press space to change selection

    As the model shows, it’s quite a time consuming process, especially when you consider that it may take a second or two to listen to the check box name and press tab. So, you can have good accessibility, and very bad usability in the same interaction. This is the state of most software at the moment, especially for screen reader users.