Furlong, N.E, Lovelace, E.A and Lovelace K.L.2000.Research methods and statistics: an integrated Approach.Fort Worth: Harcourt College. Graziano, A.M.and Raulin, M.L. 2007.Research methods: a process of inquiry.New Jersey: Pearson Education. Guilford, J.P.and B.Fruchter.1978.Fundamental Statistics in Psychology and Education.Sixth edition.Singapore: McGraw-Hill, Inc. Kumar, R.1996.Research methodology : a step-by-step guide for beginners.London:Sage. Lomax, R.G.2001.An introduction to Statistical Concepts for Education and Behavioral Sciences.NJ: Lawrence Erlbaum Associates, Inc., Publishers