Computer Program Exchange AlphaTest: A Windows Program for Tests of Hypotheses About Coefficient Alpha Gary J. Lautenschlager, University of Georgia Adam W. Meade, North Carolina State University
Description Coefficient alpha continues to serve as a valuable tool in both research and practice. Currently, there are over 6,600 direct references to Cronbach’s (1951) seminal article (Thomson ISI citation search, July 27, 2007), and numerous other publications often cite secondary sources in support of the use of coefficient alpha. Although most statistical packages offer computation of coefficient alpha, no widely available package incorporates tests comparing two or more alpha values. One may be interested in testing hypotheses among values for coefficient alpha in a variety of contexts (e.g., Feldt, 1980; Hakstian & Whalen, 1976; Meade, Michels, & Lautenschlager, 2007; Woodruff & Feldt, 1986). An example research question for independent group comparisons might be ‘‘Does internal consistency vary for different populations/studies or across age/grade levels?’’ Such questions may also be important in meta-analyses. For a dependent group analysis, a potential research question might be ‘‘Does reducing test length or changing mode of item presentation significantly impact internal consistency?’’ Although a Fortran program was developed for this purpose and made available by Lautenschlager (1989; Merino & Lautenschlager, 2003), it is not very accessible to users. The new AlphaTest program provides a user-friendly Windows interface for testing hypotheses based on the formula presented in Feldt, Woodruff, and Salih (1987) to allow tests for equivalence among a user-defined set of coefficient alpha values. In addition, a superior algorithm based on the incomplete gamma integral is used to evaluate the upper tail probability of the obtained chi-square value (L. Wilkinson, personal communication, July 10, 2007). The user is cautioned to keep in mind the assumptions of the various statistical tests of coefficient alpha (Feldt et al., 1987) and to be aware that multiple, and especially follow-up, tests may require error-rate control.
Availability The program and documentation are available as a free self-installing executable file that works on any version of Windows with Microsoft .NET Framework 2.0 (or later) installed. Both English and Spanish (C. Merino, personal communication, August 13, 2007) versions are available for download at http://www4.ncsu.edu/∼awmeade/Links.htm or by contacting either author. Applied Psychological Measurement, Vol. XX No. X, Month XXXX, X–XX DOI: 10.1177/0146621607312307 Ó Sage Publications
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Volume XX Number X Month 200X APPLIED PSYCHOLOGICAL MEASUREMENT
References Cronbach, L. J. (1951). Coefficient alpha and the internal structure of tests. Psychometrika, 16, 297-334. Feldt, L. S. (1980). A test of the hypothesis that Cronbach’s alpha reliability coefficient is the same for two tests administered to the same sample. Psychometrika, 45, 99-105. Feldt, L. S., Woodruff, D. J., & Salih, F. A. (1987). Statistical inference for coefficient alpha. Applied Psychological Measurement, 11, 93-103. Hakstian, A. R., & Whalen, T. E. (1976). A k-sample significance test for independent alpha coefficients. Psychometrika, 41, 219-231. Lautenschlager, G. J. (1989). ALPHATST: Testing for differences in values of coefficient alpha. Applied Psychological Measurement, 13, 284. Meade, A. W., Michels, L. C., & Lautenschlager, G. J. (2007). Are Internet and paper-and-pencil personality tests truly comparable? An experimental design
measurement invariance study. Organizational Research Methods, 10, 322-345. Merino, C., & Lautenschlager, G. (2003). Comparacio´n estadı´stica de la confiabilidad alfa de Cronbach: Aplicaciones en la medicio´n educacional y psicolo´gica [Statistical comparisons of Cronbach’s coefficient alpha: Applications in educational and psychological measurement]. Revista de Psicologı´a, 12(2), 127-136. Woodruff, D. J., & Feldt, L. S. (1986). Tests for equality of several alpha coefficients when their sample estimates are dependent. Psychometrika, 51, 393-413.
Author’s Address Address correspondence to Gary J. Lautenschlager, University of Georgia, Department of Psychology, Athens, GA 30602-3013; e-mail:
[email protected].
