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Cronbach's Alpha if item deleted

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Cronbach's Alpha if item deleted

Steph Auty
Hi,

I am using Cronbach's alpha to test the reliability of an index I want to
create. I am getting values of around 0.9 which I am very happy with, but
sometimes SPSS says that alpha would be improved if I removed one of the
variables. What sort of cut-off point should I use for this? Some of the
improvements are very small (e.g. 0.002). Is it worth removing these
questions?

I have several datasets each asking a range of questions which overlap
quite a lot. In one case, even though an improvement is very small, it
would make an improvement to remove it in every dataset which uses it.
Would this mean I should remove it even if just looking at one dataset I
wouldn't?

Thanks in advance for any help offered.
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Re: Cronbach's Alpha if item deleted

Stephen Brand
Steph,

If the increment in alpha is very small, you might want to use this
information to shorten your measure in future studies.  The benefit of
cutting the item is not so much that alpha goes up but that you make the
survey go faster for the participants without losing information.

HTH,

Stephen Brand

Stephen Brand, Ph.D.
Associate Professor (Research)
NCPE-SP, University of Rhode Island
Kingston, Rhode Island

-----Original Message-----
From: SPSSX(r) Discussion [mailto:[hidden email]] On Behalf Of
Steph Auty
Sent: Monday, July 31, 2006 11:00 AM
To: [hidden email]
Subject: Cronbach's Alpha if item deleted

Hi,

I am using Cronbach's alpha to test the reliability of an index I want
to
create. I am getting values of around 0.9 which I am very happy with,
but
sometimes SPSS says that alpha would be improved if I removed one of the
variables. What sort of cut-off point should I use for this? Some of the
improvements are very small (e.g. 0.002). Is it worth removing these
questions?

I have several datasets each asking a range of questions which overlap
quite a lot. In one case, even though an improvement is very small, it
would make an improvement to remove it in every dataset which uses it.
Would this mean I should remove it even if just looking at one dataset I
wouldn't?

Thanks in advance for any help offered.
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