5-Cronbach, L. J. (2004)."My current thoughts on Coefficient Alpha and successor procedures". Educational and Psychological Measurement, 64, 391-418.
6-Hair, J. F., Jr., Black,W. C., Babin, B. J., & Anderson, R. E. (2010).Multivariate dataanalysis.(7th Edition). Upper Saddle River: Prentice Hall.
7-Helms, J. E., Henze, K. T., Sass, T. L., & Mifsud, V. A. (2006). "Treating Cronbach’s alpha reliability coefficients as data in counseling research".The Counseling Psychologist.34 (5).630-660.
8- Joval , P.G., Zheng , C.N. and Philip , S.W.(2009)."Fault Detection of Drinking of Water Treatment process Using PCA and Hotelling,s chart ". World Academy of science , Engineering and Technology , vol . 50 pp.970-975.
9-Montgomery, D. C. (2009)."Introduction to Statistical Quality Control".6th Edition. John Wily & S