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Re: st: Does there exist measurement error when I got high Cronbach's alpha?


From   Amir Sariaslan <amir.sariaslan@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Does there exist measurement error when I got high Cronbach's alpha?
Date   Sat, 16 Jul 2011 15:06:11 +0200

Dear Sharon,

1) I would be very cautious of interpreting Chronbach's alpha due to
its numerous flaws (see i.e. Raykov, 1997). If nothing else, you're
dealing with a multidimensional (five factors) instrument while the
measure assumes unidimensionality.

2) Yes, Stata does indeed listwise delete your missing cases as a
default. Recoding your missing cases to negative values will starkly
bias the results and is probably more misleading than anything else.
There are alternative ways of handling missing cases, one being
imputation. In this case, for what it's worth, I would think that
listwise deleting the cases is more appropriate than to recoding them
to arbitrary negative values.

Sincerely,
Amir

Reference:
Raykov, T. (1997): "Scale Reliability, Cronbach's Coefficient Alpha,
and Violations of Essential Tau-Equivalence with Fixed Congeneric
Components". Multivariate Behavioral Research, vol. 32(4), pp. 329-53

On Sat, Jul 16, 2011 at 2:46 PM, xueliansharon <xuelianstata@gmail.com> wrote:
> Dear all:
>
> I got quite high Cronbach's alphas (0.9) for five-factor personality traits
> (extraversion, agreeableness, conscientiousness, emotional stability and
> intellect). With such high values, can I argue that there may still exist
> measurement errors in the measures for five-factor personality traits?
>
> Another question is about the computation of Cronbach's alpha. I got
> different values of alpha when using different computation procedure: the
> key difference happened when I recoded the responses of five factors
> personality to "missing values" when the original responses were "-3" (i.e.
> no questions answered) or "-2" (i.e. information incomplete). For example,
> for the extraversion measure, the range of the score should be 5 to 50
> points, when I recoded the response "-3" or "-2" to "missing value", the
> sample size was reduced by around 680, since the number of observations who
> didn't answer the questions about extraversion or didn't provide complete
> information for each item were 680, and the alpha coefficient fell from 0.9
> to 0.6. So is it correct to do such recoding when computing alpha
> coefficients?
>
> Your response is greatly appreciated.
>
> Thanks & Regards,
> Sharon
>
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