cronbach's alpha

[Najmul Hoda]

Dear Members

I have some queries regarding cronbach's alpha.

1.  How significant is the value of cronbach's alpha?

2.  What if the value comes to less than 0.7? 

Thanks

[VARUN ARORA]

For Cronbach alpha: the generally agreed upon criteria  for scale reliability is its cut-off value 0.7 (Nunally, 1978). though there are some workers viz. Moss et al. (1998) who have also supported the view that Cronbach alpha value above 0.6 is generally acceptable. Hair (1998) has also supported the view that in a study with small sample size, low Cronbach alpha scores such as 0.6 can be taken as the measure of acceptable. For subscale mesaures, Nagpal has suggested use of cut-off value of 0.6.

1. Nunally JC. Psychometric Theory, McGraw-Hill, New York, 1978.

2. Moss SC, Prosser H, Costello H, et al. Reliability and validity of the PAS-ADD Checklist for detecting psychiatric disorders in adults with intellectual disability. Journal of Intellectual Disability Research 1998; 42, 173-183.

3. Hair J, Anderson R, Tatham R and Black W.. Multivariate Data Analysis. NJ: Pearson/Prentice Hall, Inc., 2006.

 4. Nagpal J, Kumar A, Kakar S, Bhartia A. The Development of ‘Quality of Life Instrument for Indian Diabetes Patients (QOLID) : A Validation and Reliability Study in Middle and Higher Income Groups. JAPI 2010; 58: 295-304. 

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VARUN ARORA
MBA (Hons.), MEARMA (Brussels),
Cert. Pub. Health (Univ. of California, Irvine)
Member, Ethical Issues Group,
European Association of Res. Managers & Adm.,
Research Consultant, APS, Lucknow, India.

[Rekha Mishra]

There are different reports about the acceptable values of alpha, ranging from 0.70 to 0.95. 2, 21, 22 A low value of alpha could be due to a low number of questions, poor interrelatedness

between items or heterogeneous constructs. For example if a low alpha is due to poor correlation between items then some should be revised or discarded. The easiest method to find them is to compute the correlation of each test item with the total score test; items with low correlations (approaching zero) are deleted. If alpha is too high it may suggest that some items are redundant as they are testing the same question but in a different guise. A maximum alpha value of 0.90 has been recommended.