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Aim and impact of random sampling

From: Detlev Fischer <fischer@dias.de>
Date: Thu, 24 Jan 2013 17:22:59 +0100
Message-ID: <51015FE3.1050301@dias.de>
To: EVAL TF <public-wai-evaltf@w3.org>
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.

Detlev

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Detlev Fischer PhD
DIAS GmbH - Daten, Informationssysteme und Analysen im Sozialen
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Received on Thursday, 24 January 2013 16:23:24 GMT

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