I agreed with Paul completely about this point. Cortina published a paper
about this issue in Journal of Applied Psychology in 1993.
____________________________________________
Peter Chen
Industrial/Organizational Psychologist and Researcher
Liberty Mutual Research Center
71 Frankland Road, Hopkinton, MA 01748 USA
Tel. (508) 435-9061 x301 Fax. (508) 435-8136
E-mail: [EMAIL PROTECTED]
Web: http://www.libertymutual.com/research
____________________________________________
-----Original Message-----
From: Paul Gardner [SMTP:[EMAIL PROTECTED]]
Sent: Thursday, December 16, 1999 11:40 PM
To: [EMAIL PROTECTED]
Cc: John Donovan; [EMAIL PROTECTED]
Subject: Re: Scale Reliability
[EMAIL PROTECTED] wrote:
>
> The fact that the shorter scale has low internal consistency
doesn't necessarily
> mean that the 4 items in question are not unidimensional. It may
just be that
> the measurement error is large relative to their covariance.
Given that the
> four items in question are drawn from a scale with established
internal
> consistency, I'd suspect they probably are measuring the same
thing - only not
> measuring it very well.
>
> purnima.
>
No, there is a flaw in the logic here. If a scale has "established
internal consistency" (usually based on a high Cronbach alpha
value), a
researcher CANNOT conclude that the items are "measuring the same
thing". All it takes for alpha to be high is that each item
correlates
well with at least some other items, but not necessarily with all of
them. Alpha is a good indicator of the relative freedom of the
items in
a scale from random measurement error. It is NOT a sound indicator
of
unidimensionality. The misconception that it is such an indicator
is
widespread.
Paul Gardner << File: Card for Paul Gardner >>
