Re: General Usability DetecVS tor

Time cannot be used as a reliable indicator of usability.

Firstly you will not get "times" that are nicely differentiated like 2mins vs 4mins

It will be more like 2.1 mins vs 2.25 mins.

Then there's the issues of when the task started, the level of verbosity of the participant
and level of success related to the completion of the task.

Finally, satisfaction plays a big part too. Just because a task takes a few extra seconds may not mean
that participants are any less satisfied with the effectiveness [their success] or efficiency [their effort] of the interface.
In fact those few extra seconds may indeed add to satisfaction in some cases and leave the participant
feeling that the interface is more usable.


So to answer your question you cannot differentiate [nor should you] accessibility and usability issues a priori.
The only way to know if issues are particular to the disabled is to test with those intended users.
That involves running a formal usability test.

Accessibility has a lot to do with the coding we use for web pages etc and that sadly is where it has
always lost traction with the wider commercial world. Until we make testing with real users the central theme then
accessibility will continue to reside in an esoteric, "not my problem" backwater as far as most corporations
are concerned.

Thanks,
Gordon. 

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  ----- Original Message ----- 
  From: Gregg Vanderheiden 
  To: w3c-wai-gl@w3.org 
  Sent: Monday, May 10, 2004 12:46 AM
  Subject: General Usability DetecVS tor


  In discussions on our last call "usability" came up since it was a question from one of our reviewers



  How do we separate

  "Accessibility / Usability problems that are specific to disabilities" 

  From

  "usability issues that are faced by all users"





  One test I have sometimes found useful in examining this question is 

     "Does it multiply the time and effort for people with disabilities by the same amount as people without disabilities?"

  If the multiplier is the same - then it may be a general usability issue.



  For example

  Good page    2 min  for  no disability

  Good page    4 min for screen reader user



  Bad page      3 min for no disability

  Bad page       6 min for screen reader user



  This bad page appears to be 50% harder for both groups.   This looks more like a general usability problem rather than accessibility since it slows everyone down by the same factor





  Another example



  Good page   2 min for no disability 

  Good page   4 min with screen reader



  Page 2  -    3 min for no disability

  Page 2  -    10 min   with screen reader. 



  Page 3  -    3 min for no disability

  Page 3  -     cannot get at some of the information with screen reader. 



  These look like accessibility problems 

  Page 2 is much more than proportionately harder (250% vs 50%)

  Page 3 is inaccessible 





  Just passing along in case it is of use to others in thinking about the problem






  Gregg

  ------------------------

  Gregg C Vanderheiden Ph.D. 
  Professor - Depts of Ind. Engr. & BioMed Engr.
  Director - Trace R & D Center 
  University of Wisconsin-Madison 
  <http://trace.wisc.edu/> FAX 608/262-8848  
  For a list of our list discussions http://trace.wisc.edu/lists/