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Re: Aim and impact of random sampling

From: Ramón Corominas <rcorominas@technosite.es>
Date: Thu, 24 Jan 2013 20:55:44 +0100
Message-ID: <510191C0.2080306@technosite.es>
To: public-wai-evaltf@w3.org
Although I did not use the words "optional/mandatory", I also commented 
in the survey that some Euracert partners will probably dislike the idea 
of having to include more pages (= more time and resources), since they 
consider that the initial structured sampling is enough in most cases, 
(that is, no significant change in the results will be obtained).

We at Technosite include the "random" part just because the website is 
evaluated over time, and thus we make clear to the clients that the 
sample will not always be the same, and therefore they will have to 
apply the accessibility criteria to the whole website. However, I agree 
that our "method" to select random pages is certainly not very scientific.

In any case, I assume that the "filter the sample" should be enough to 
eliminate the problem of time/resources. However,

My vote: it should be an optional step.


Aurélien wrote:

> +1 that the sense of the comment I made on the survey I think this need 
> to be an option
 > Detlev wrote:
>> The assumption has been that an additional random sample will make 
>> sure that a tester's intitial sampling of pages has not left out pages 
>> that may expose problems no present in the intitial sample.
>> That aim in itself is laudable, but for this to work, the sampling 
>> would need to be
>> 1. independent of individual tester choices (i.e., automatic) -
>>    which would need a definition, inside the methodology, of a
>>    valid approach for truly random sampling. No one has even hinted on
>>    a reliable way to do that - I believe there is none.
>>    A mere calculaton of sample size for a desired level of confidence
>>    would need to be based to the total number of a site's pages *and*
>>    page states - a number that will usually be unknown.
>> 2. Fairly represent not just pages, but also page states.
>>    But crawling a site to derive a collection of URLS for
>>    random sampling is not doable since many states (and there URLs or
>>    DOM states) only come about as a result of human input.
>> I hope I am not coming across as a pest if I say again that in my 
>> opinion, we are shooting ourselves in the foot if we make random 
>> sampling a mandatory part of the WCAG-EM. Academics will be happy, 
>> practitioners working to a budget will just stay away from it.
Received on Thursday, 24 January 2013 19:57:18 UTC

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