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SIGIA-L Mail Archives: RE: [Sigia-l] Card Sorting: How Many Users to Test

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

From: Jonathan Baker-Bates (Jonathan.Baker-Bates_at_oyster.com)
Date: Mon Jul 19 2004 - 08:01:00 EDT


> > You must test fifteen users to reach a correlation of 0.90,

I'm unclear how these correlations square with the "who to test" issue.
Most clients have desired segments they want represented in their
testing (Teens, Housewives, Bald Women... OK maybe not that divergent,
but sub-sections of their customer base), so is he talking about the
number of users you have in the *same* segment here? If in a test group
of 20, the Asian Doctors group things radically differently from the
Truck Drivers and Tea Ladies, surely the fact that there are only five
Asian Doctors is significant.

Jonathan

 

> -----Original Message-----
> From: sigia-l-admin_at_asis.org [mailto:sigia-l-admin_at_asis.org]
> On Behalf Of Eric Scheid
> Sent: 19 July 2004 12:36
> To: sigia l
> Subject: [Sigia-l] Card Sorting: How Many Users to Test
>
>
> 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.
>
>
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