RE: [Sigia-l] Card Sorting: How Many Users to Test

From: Boniface Lau (boniface_lau_at_compuserve.com)
Date: Mon Jul 19 2004 - 20:12:40 EDT

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> From: Eric Scheid
>
> ahh ... surely there's something controversial in Jakob's
> latest AlertBox...
>
>
> http://www.useit.com/alertbox/20040719.html
>
> > You must test fifteen users to reach a correlation of 0.90, which
> > is a more comfortable place to stop. After fifteen users,
> > diminishing returns set in and correlations increase very little:
> > testing thirty people gives a correlation of 0.95 -- certainly
> > better, but usually not worth twice the money. There are hardly
> > any improvements from going beyond thirty users: you have to test
> > sixty people to reach 0.98, and doing so is definitely wasteful.

Why did you think the above was controversial?

Boniface

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