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Re: ISSUE-30 counter-proposal

From: Philip Taylor <pjt47@cam.ac.uk>
Date: Sun, 14 Feb 2010 16:30:10 +0000
Message-ID: <4B782512.4070106@cam.ac.uk>
To: Shelley Powers <shelleypowers@burningbird.net>
CC: Ian Hickson <ian@hixie.ch>, public-html@w3.org
Shelley Powers wrote:
> Ian Hickson wrote:
>> Here's a counter-proposal for ISSUE-30:
>>
>> == Summary ==
>>
>> The longdesc="" attribute does not improve accessibility in practice 
>> and should not be included in the language.
>>
>> == Rationale ==
>>
>> Several studies have been performed. They have shown that:
>>
>> * The longdesc="" attribute is extremely rarely used (on the order of 
>> 0.1% in one study). [http://blog.whatwg.org/the-longdesc-lottery]
>> * When used, longdesc="" is extremely rarely used correctly (over 99% 
>> were incorrect in a study that only caught the most obvious errors 
>> [http://blog.whatwg.org/the-longdesc-lottery]; the correct values were 
>> below the threshold of statistical significance on another study that 
>> examined each longdesc="" by hand 
>> [http://wiki.whatwg.org/wiki/Longdesc_usage]).
>> * Most users (more than 90%) don't want the interaction model that 
>> longdesc="" implies. 
>> [http://webaim.org/projects/screenreadersurvey2/#images]
>> * Users that try to use longdesc="" find it doesn't work ("Who uses 
>> this kind of thing? In my experience [...] it just didn't work. There 
>> was no description.") [http://www.cfit.ie/html5_video/Longdesc_IDC.wmv].
>>   
> 
> I'll let the accessibility folks respond to the accessibility components 
> of your proposal, but we've had discussions in the past about your 
> "studies", and the flaws associated with them.
> 
> First of all, you've not provided access to the same data, so your 
> results cannot be confirmed or denied.
> 
> Secondly, you have a bias in the results, and bias has been shown to
> compromise the integrity of studies.
> [...]

The original source of the 0.1% usage data in 
<http://blog.whatwg.org/the-longdesc-lottery> is the public web, so the 
results can be easily checked by running independent studies over other 
subsets of the web. E.g. with the pages provided by 
<http://www.dotnetdotcom.org/>, 0.5% (2288 out of 425532) have at least 
one <img longdesc>. (The raw parsed attribute value data is at 
<http://philip.html5.org/data/longdesc-raw.txt>, if anyone wants to look 
in more detail). The exact numbers depend on how you sample the web, but 
I'm not aware of any wide-scale survey of pages that has produced 
significantly different results.

http://wiki.whatwg.org/wiki/Longdesc_usage is already entirely 
independent of Google, and comes from public data - the original listing 
of pages came from dmoz.org, and Andrew Sidwell examined each of the 
pages to derive the results. The WebAIM survey and the user testing 
videos were also developed independently.

(I'm not saying any of this data is perfect and infallible, or that it 
can't be interpreted in different ways - I'm just saying that claims of 
non-reproducibility and of personal bias in the collection of the data 
seem to be inaccurate.)

-- 
Philip Taylor
pjt47@cam.ac.uk
Received on Sunday, 14 February 2010 16:30:45 GMT

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