Öğrencilerin Sınıf Değerlendirme Atmosferine Yönelik Algılarının Matematik Kaygılarını Yordama Gücü

In this study, it was aimed to determine the predictive power of students’ perceptions of classroom assessment environment for their mathematics anxiety. A correlational model was employed in this study, which was carried out with 410 high school students in the provinces of Diyarbakir in Turkey in the fall of 2014–2015. The Mathematics Anxiety Scale which was developed by Bindak (2005) was employed in the study to measure the students’ math anxiety. Then, in order to determine the students’ perceptions of the classroom assessment environment, the Classroom Assessment Environment Scale, which was developed by Ilhan and Cetin (2014a), was used. The relationships between students’ mathematics anxiety and their perceptions of the classroom assessment environment were investigated via correlation and multiple regression analysis. The results obtained from the correlation analysis demonstrated that learning oriented assessment environment was negatively related to mathematics anxiety. In contrary, performance oriented assessment environment was positively related to mathematics anxiety. As a result of regression analysis, it was determined that students’ perceptions of the classroom assessment environment explain 18% of the total variance on their mathematics anxiety.

The Predictive Power of Students’ Perceptions of Classroom Assessment Environment for Their Mathematics Anxiety

In this study, it was aimed to determine the predictive power of students’ perceptions of classroom assessment environment for their mathematics anxiety. A correlational model was employed in this study, which was carried out with 410 high school students in the provinces of Diyarbakir in Turkey in the fall of 2014–2015. The Mathematics Anxiety Scale which was developed by Bindak (2005) was employed in the study to measure the students’ math anxiety. Then, in order to determine the students’ perceptions of the classroom assessment environment, the Classroom Assessment Environment Scale, which was developed by Ilhan and Cetin (2014a), was used. The relationships between students’ mathematics anxiety and their perceptions of the classroom assessment environment were investigated via correlation and multiple regression analysis. The results obtained from the correlation analysis demonstrated that learning oriented assessment environment was negatively related to mathematics anxiety. In contrary, performance oriented assessment environment was positively related to mathematics anxiety. As a result of regression analysis, it was determined that students’ perceptions of the classroom assessment environment explain 18% of the total variance on their mathematics anxiety.
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  • Ahmed, W., Minnaert, A., Kuyper, H., & van der Werf, G. (2013). Reciprocal relationships between math self-concept and math anxiety. Learning and Individual Differences, 22(3), 385-389. http://dx.doi.org/10.1016/j.lindif.2011.12.004
  • Alam, H.M.A., & Nadim, D. (2014). Mathematics anxiety in relation to achievement of mathematics among Urdu medium high school students in Hyderabad. Journal of Advanced Studies in Education and Management, 1(1), 42-46. Retrieved from http://www.bcetldh.org/wp-content/uploads/2014/09/journal.pdf
  • Alexander, L., & Cobb, R. (1989). Identification of the dimensions and predictors of math anxiety among college students. Journal of Human Behavior and Learning, 4(1), 25-32. Retrieved from http://files.eric.ed.gov/fulltext/ED251320.pdf
  • Alkan, V. (2013). Reducing mathematics anxiety: The ways implemented by teachers at primary schools in Turkey. International J. Soc. Sci. & Education, 3(3), 795-807. Retrieved from http://ijsse.com/sites/default/files/issues/2013/v3i3/Paper-25.pdf
  • Alkharusi, H. (2008). Effects of classroom assessment practices on students' achievement goals. Educational Assessment, 13(4), 243-266. http://dx.doi.org/10.1080/10627190802602509
  • Alkharusi, H. (2010). Teachers’ assessment practices and students’ perceptions of the classroom assessment environment. World Journal on Educational Technology, 2(1), 27-41. Retrieved from http://www.world-education-center.org/index.php/wjet/article/view/160/pdf_8
  • Alkharusi, H., Aldhafri, S., Alnabhani, H., & Alkalbani, M. (2014). Modeling the relationship between perceptions of assessment tasks and classroom assessment environment as a function of gender. Asia Pacific Education Researcher, 21(3), 93-104. http://dx.doi.org/10.1007/s40299-013-0090-0
  • Ames, C. (1992). Classrooms: Goals, structures, and student motivation. Journal of Educational Psychology, 84(3), 261-271. http://dx.doi.org/10.1037/0022-0663.84.3.261
  • Ashcraft, M.H., Krause, J.A., & Hopko, D.R. (2007). Is math anxiety a mathematical learning disability? In D.B. Berch & M.M.M. Mazzocco (Eds.), Why is math so hard for some children? (2nd ed., pp. 329-348). Baltimore, MD: Brookes Publishing.
  • Ashcraft, M.H., & Moore, A.M. (2009). Mathematics anxiety and the affective drop in performance. Journal of Psychoeducational Assessment, 27(3), 197-205. http://dx.doi.org/10.1177/0734282908330580
  • Baek, S., & Choi, H. (2002). Relationship between students perceptions of classroom environment and their academic achievement in Korea. Asian pacific Education Review, 3(1), 125-135. http://dx.doi.org/10.1007/BF03024926
  • Banks, S.R. (2012). Classroom assessment: Issues and practices (2nd ed.). Long Grove, IL: Waveland Press Inc.
  • Barth, J.M., Dunlap, S.T., Dane, H., Lochmanb, J.E., & Wells, K.C. (2004). Classroom environment influences on aggression, peer relations, and academic focus. Journal of School Psychology, 42(2), 115-133. http://dx.doi.org/10.1016/j.jsp.2003.11.004
  • Baymur, F. (1994). General psychology (11th ed.). Istanbul: İnkılâp Publishing.
  • Bindak, R. (2005). Mathematics anxiety scale for primary school students. Science and Engineering Journal of Firat University, 17(2), 442-448. Retrieved from http://www.salihyildiz.net/wp-content/uploads/2013/03/RBindak-MatKayg%C4%B1s%C4%B1.pdf
  • Brookhart, S.M., & DeVoge, J.G. (1999) Testing a theory about the role of classroom assessment in student motivation and achievement. Applied Measurement in Education, 12(4), 409-425. http://dx.doi.org/10.1207/S15324818AME1204_5
  • Brookhart, S.M., Walsh, J.M., & Zientarski, W.A. (2006). The dynamics of motivation and effort for classroom assessment in middle school science and social studies. Applied Measurement in Education, 19(2), 151-184. http://dx.doi.org/10.1207/s15324818ame1902_5
  • Buhagiar, M.A. (2007) Classroom assessment within the alternative assessment paradigm: Revisiting the territory. The Curriculum Journal, 18(1), 39-56. http://dx.doi.org/10.1080/09585170701292174
  • Buldur, S. (2014). The investigation of the relationship between the students’ perceptions about the classroom assessment environment and their achievement-goal orientations: Gender perspective. Education and Science, 39(176), 213-225. http://dx.doi.org/10.15290/EB.2014.3730
  • Buyukozturk, S. (2010). A manual on data analysis in social sciences (11th ed.). Ankara: Pegem Academy Publishing.
  • Chaman, M., & Callingham, R. (2013). Relationship between mathematics anxiety and attitude toward mathematics among Indian students. Mathematics education: Yesterday, today and tomorrow. Paper presented at the 36th Annual Conference of the Mathematics Education Research Group of Australasia, Melbourne, Victoria. Retrieved from http://www.merga.net.au/documents/Chaman_et_al_MERGA36-2013.pdf
  • Creswell, J.W. (2012). Educational research: Planning, conducting, and evaluating quantitative and qualitative research (4th ed.) Boston: Pearson.
  • Crooks, T.J. (1988). The impact of classroom evaluation practices on students. Review of Educational Research, 58(4), 438-481. http://dx.doi.org/10.3102/00346543058004438
  • Cuoco, A., Goldenberg, E.P., & Mark, J. (1996). Habits of mind: An organizing principle for mathematics curricula. The Journal of Mathematical Behavior, 15(4), 375-402. http://dx.doi.org/10.1016/S0732-3123(96)90023-1
  • Dart, B., Burnett, P.C., Boulton-Lewis, G., Campbell, J., Smith, D., & McCrindle, A. (1999). Classroom learning environments and students’ approaches to learning. Learning Environments Research, 2(2), 137-56. http://dx.doi.org/10.1023/A:1009966107233
  • Dewine, A., Fawcett, K., Szűcs, D., & Dowker, A. (2012). Gender differences in mathematics anxiety and the relation to mathematics performance while controlling for test anxiety. Behavioral and Brain Functions, 8(33), 1-9. http://dx.doi.org/10.1186/1744-9081-8-33
  • Diekhoff, G.M., & Wigginton, P.K. (1992). Assessing college classroom environment using free description: A methodological demonstration (ERIC Document Reproduction Service No. ED 337 071). Retrieved from http://files.eric.ed.gov/fulltext/ED337071.pdf
  • Dorman, J.P. (2001). Sociations between classroom environment and academic efficacy. Learning Environments Research, 4(3), 243-257. http://dx.doi.org/10.1023/A:1014490922622
  • Eden, C., Heine, A., & Jacobs, A.M. (2013). Mathematics anxiety and its development in the course of formal schooling-A review. Psychology, 4(6), 27-35. http://dx.doi.org/10.4236/psych.2013.46A2005
  • Elton, L.R.B., & Laurillard, D.M. (1979). Trends in research on student learning, Studies in Higher Education, 4(1), 87-102. http://dx.doi.org/10.1080/03075077912331377131
  • Fornell, C., & Larcker, D.F. (1981). Evaluating structural equation models with unobservable variables and measurement error. Journal of Marketing Research, 18(1), 39-50. http://dx.doi.org/10.2307/3151312
  • Fraenkel, J.R., Wallend, N.E., & Hyun, H.H. (2012). How to design and evaluate research in education (8th ed). New York: McGraw Hill.
  • Fraser, B.J. (1998). The birth of a new journal: Editor’s introduction. Learning Environments Research, 1(1), 1-5. http://dx.doi.org/10.1023/A:1009994030661
  • Fraser, B.J., Nash, R., & Fisher, D.L. (1983) Anxiety in
  • science classrooms: Its measurement and relationship to classroom environment. Research in Science & Technological Education, 1(2), 201-208. http://dx.doi.org/10.1080/0263514830010208
  • Frenzel, A.C., Pekrun, R., & Goetz, T. (2007). Perceived learning environment and students’ emotional experiences: A multilevel analysis of mathematics classrooms. Learning and Instruction, 17(5), 478-493. http://dx.doi.org/10.1016/j.learninstruc.2007.09.001
  • Furner, J.M., & DeHass, A.G. (2011). How do students’ mastery and performance goals relate to math anxiety? Eurasia Journal of Mathematics, Science & Technology Education, 7(4), 227-242. Retrieved from http://www.ejmste.com/v7n4/EURASIA_v7n4_Furner.pdf
  • Goh, S.C., & Fraser, B.J. (1998). Teacher interpersonal behaviour, classroom environment and student outcomes in primary mathematics in Singapore. Learning Environments Research, 1(2), 199-229. http://dx.doi.org/10.1023/A:1009910017400
  • Gourgey, A.F. (1984, April). The relationship of misconceptions about math and mathematical self-concept to math anxiety and statistics performance. Paper presented at the Annual Meeting of the American Educational Research Association, New Orleans, LA. (ERIC Document Reproduction Service No., ED254417). Retrieved from http://files.eric.ed.gov/fulltext/ED254417.pdf
  • Greene, B.A., Miller, R.B., Crowson, H.M., Duke, B.L., & Akey, K.L. (2004). Predicting high school students cognitive engagement and achievement: Contributions of classroom perceptions and motivation. Contemporary Educational Psychology, 29(4), 462-482.http://dx.doi.org/10.1016/j.cedpsych.2004.01.006
  • Harbaugh, A.G., & Cavanagh, R.F. (2012, December) Associations between the classroom learning environment and student engagement in learning 2: A structural equation modeling approach. Paper Presented at the AARE-APERA 2012, Sydney. Retrieved from http://files.eric.ed.gov/fulltext/ED542256.pdf
  • Harty, H., & Hassan, H.A. (1983). Student control ideology and the science classroom environment in urban secondary schools of Sudan. Journal of Research in Science Teaching, 20(7), 851-859. http://dx.doi.org/10.1002/tea.3660200907
  • Hembree, R. (1990). The nature, effects, and relief of mathematics anxiety. Journal for Research in Mathematics Education, 21(1), 33-46. http://dx.doi.org/10.2307/749455
  • Ilhan, M., & Cetin, B. (2014a). Development of classroom assessment environment scale (CAES): Validity and reliability study. Education and Science, 39(176), 31-50. http://dx.doi.org/10.15390/EB.2014.3334
  • Ilhan, M., & Cetin, B. (2014b). An analysis of the relationship between academic burnout and classroom assessment environment. Education and Science, 39(176), 51-68. http://dx.doi.org/10.15390/EB.2014.3335
  • Kargar, M., Tarmizi, R.A., & Bayat, S. (2010). Relationship between mathematical thinking, mathematics anxiety and mathematics attitudes among university students. Procedia Social and Behavioral Sciences, 8 537-542. http://dx.doi.org/10.1016/j.sbspro.2010.12.074
  • Kent, H., & Fisher, D. (1997, March). Associations between teacher personality and classroom environment. Paper presented at the Annual Meeting of the American Educational Research Association, Chicago. Retrieved from http://www2.sfasu.edu/cte/Michelle_Files/HMS_300_Web_Content/Teacher_Personality.pdf
  • Kose, E., & Kucukoglu, A. (2008). Evaluation of class learning environment in faculties of education in terms of some variables. Ahi Evran University Journal of Kırşehir Education Faculty, 10(3), 61-73. Retrieved from http://kefad.ahievran.edu.tr/archieve/pdfler/Cilt10Sayi3/JKEF_10_3_2009_61_73.pdf
  • Kurt, H., Ekici, G., Gokmen, A., Aktaş, M., & Aksu, O. (2013). The effect of learning styles on secondary education students’ perception of classroom environment of biology laboratory (Kolb learning style model sample). Turkish Studies, 8(6), 157-177. http://dx.doi.org/10.7827/TurkishStudies.4831
  • Kunkul, T. (2008). The analysis of the relationship between students’ participation level of classroom activities and classroom atmosphere. Master Dissertation, CukurovaUniversity, Institute of Social Sciences, Adana, Turkey.
  • Lau, K.L., & Lee, C.K. (2008). Examining Hong Kong students’ achievement goals and their relations with students’ perceived classroom environment and strategy use. Educational Psychology: An International Journal of Experimental Educational Psychology, 28(4), 357-372. http://dx.doi.org/10.1080/01443410701612008
  • Lawrence, F.P., & Welch, W.W. (1983). Student perceptions of science classes taught by males and females. Journal of Research in Science Teaching, 20(7), 655-662. http://dx.doi.org/10.1002/tea.3660200706
  • Lazarus, M. (1974). Mathophobia: Some personal speculations. National Elementary Principal, 53(2), 16-22. Retrieved from http://connection.ebscohost.com/c/articles/18647128/mathophobia-some-personal-speculations
  • Lim, S.Y., & Chapman, E. (2013). Identifying affective domains that correlate and predict mathematics performance in high-performing students in Singapore. Educational Psychology: An International Journal of Experimental Educational Psychology, Retrieved from http://www.tandfonline.com/doi/pdf/10.1080/01443410.2013.860221
  • Ma, X. (1999). A meta-analysis of the relationship between anxiety and toward mathematics and achievement in mathematics. Journal for Research in Mathematics Education, 30(5), 502-540. Retrieved from http://www.nctm.org/publications/article.aspx?id=17678
  • Mahigir, F., Venkatesh Kumar, G., & Ayat, K. (2012). Parent’s socio economic background, mathematics anxiety and academic achievement. International Journal of Education Administration and Policy Studies, 4(8), 177-180. http://dx.doi.org/10.5897/IJEAPS11.077
  • Maloney, E.A., Waechter, S., Risko, E.F., & Fugelsang, J.A (2012). Reducing the sex difference in math anxiety: The role of spatial processing ability. Learning and Individual Differences, 22(3), 380-384. http://dx.doi.org/10.1016/j.lindif.2012.01.001
  • Marsh, G.E., & Tapia, M. (2002, November). Feeling good about mathematics: Are there sex differences? Paper presented at the Annual meeting of the Mid-South Educational Research Association. Chattanooga, TN. Retrieved from http://files.eric.ed.gov/fulltext/ED474446.pdf
  • McLeod, D.B. (1992). Research on affect in mathematics education: A reconceptulization. In D.A. Grouws (Ed.), Handbook of research on mathematics teaching and learning (pp. 575-596). New York: Macmillan.
  • McMillan, J.J., & Schumacher, S. (2010). Research in education evidence based inquiry. Boston: Pearson.
  • McMillan, J.H., & Workman, D.J. (1998). Classroom assessment and grading practices: A review of the literature. Richmond, VA: Metropolitan Educational Research Consortium. (ERIC Document Reproduction Service No., ED 453263). Retrieved from http://files.eric.ed.gov/fulltext/ED453263.pdf
  • Meece, J.L., Wigfield, A., & Eccles, J.S. (1990). Predictors of math anxiety and its influence on young adolescents’ course enrollment intentions and performance in mathematics. Journal of Educational Psychology, 82(1), 60-70. http://dx.doi.org/10.1037/0022-0663.82.1.60
  • Mesa, V. (2012). Achievement goal orientations of community college mathematics students and the misalignment of instructor perceptions. Community College Review, 40(1), 46-74. http://dx.doi.org/10.1177/0091552111435663
  • Miller, L.D., & Mitchell, C.E. (1994). Mathematics anxiety and alternative methods of evaluation. Journal of Instructional Psychology, 21(4), 353-359.
  • Mutodi, P., & Ngirande, H. (2014). Exploring mathematics
  • anxiety: Mathematics students’ experiences. Mediterranean Journal of Social Sciences, 5(1), 283-294. Retrieved from http://mcser-org.ervinhatibi.com/journal/index.php/mjss/article/download/1905/1904
  • National Council of Teachers of Mathematics. (1995). Mathematics anxiety. [Supplemental Brochure]. Reston, VA: Author.
  • Ornstein, A.C., & Hunkins, F.P. (2009). Curriculum: Foundation, principles, and issues (5th ed.). Boston, MA: Allyn & Bacon.
  • Pallant, J. (2005). SPSS survival manual: A step by step guide to data analysis using SPSS for windows (2nd ed.). Australia: Australian Copyright.
  • Pedhazur, E.J., & Schmelkin, L.P. (1991). Measurement, design, and analysis: An integrated approach. Hillsdale, NJ: Lawrence Erlbaum Associates.
  • Popilskis, L.B. (2013). The link between students’ achievement goals and perceptions of the classroom environment. Doctoral Dissertation, Fordhman University, New York. Retrieved from http://fordham.bepress.com/dissertations/AAI3558542/
  • Pulvers, K., & Diekhoff, G.M. (1999). The relationship between academic dishonesty and college classroom environment. Research in Higher Education, 40(4), 487-498. http://dx.doi.org/10.1023/A:1018792210076
  • Rampersad, R. (2003). Mathematics anxiety and achievement in mathematics, Master dissertation, Retrieved from http://digitool.library.mcgill.ca/webclient/StreamGate?folder_id=0&dvs=1415965251963~450
  • Richardson, F.C., & Suinn, R.M. (1972). The mathematics anxiety rating scale: Psychometric data. Journal of Counseling Psychology, 19(6), 551-554. http://dx.doi.org/10.1037/h0033456
  • Rodriguez, M.C. (2004). The role of classroom assessment in student performance on TIMSS. Applied Measurement in Education, 17(1), 1-24. http://dx.doi.org/10.1207/s15324818ame1701_1
  • Shields, D.J. (2006). Causes of mathematics anxiety. The student perspective. Unpublished Doctoral Dissertation, Indiana University of Pennyslvania, Indiana.
  • Steele, E., & Arth, A. (1998). Lowering anxiety in the math curriculum. Education Digest, 63(7), 18-24. Retrieved from http://connection.ebscohost.com/c/articles/341842/lowering-anxiety-math-curriculum
  • Stevens, J.P. (2009). Applied multivariate statistics for the social sciences (5th ed.). New York: Routledge.
  • Stiggins, R., & Chappuis, J. (2005). Using student-involved classroom assessment to close achievement gaps. Theory Into Practice, 44(1), 11-18. http://dx.doi.org/10.1207/s15430421tip4401_3
  • Tabachnick, B.G., & Fidell, L.S. (2013). Using multivariate statistics (6th ed.). Boston, Pearson Education, Inc.
  • Talton, E.L., & Simpson, R.D. (1987). Relationships of attitude toward classroom environment with attitude toward and achievement in science among tenth grade biology students. Journal of Research in Science Teaching, 24(6), 507-525. http://dx.doi.org/10.1002/tea.3660240602
  • Taylor, B.A. (2014). The influence of classroom environment on high school students mathematics anxiety and attitudes. Doctoral Dissertation, Curtin University of Technology, Bentley, Western Australia, Australia. Retrieved from http://espace.library.curtin.edu.au/R/?func=dbin-jump-full&object_id=15708&local_base=GEN01-ERA02
  • Taylor, B.A., & Fraser, B.J. (2013). Relationships between learning environment and mathematics anxiety. Learning Environment Research, 16(2), 297-313. http://dx.doi.org/10.1007/s10984-013-9134-x
  • Tobias, S., & Weissbrod, C. (1980). Anxiety and mathematics: An update. Harvard Educational Review, 50(1), 63-70. Retrieved from http://her.hepg.org/content/xw483257j6035084.pdf
  • Tooke, D.J.L., & Leonard, C. (1998). Effectiveness of a mathematics methods course in reducing mathematics anxiety of preservice elementary teachers. School Science and Mathematics, 98(3), 136-142. http://dx.doi.org/10.1111/j.1949-8594.1998.tb17406.x
  • Uredi, I., & Uredi, L. (2005). The predictive power of self-regulation strategies and motivational beliefs on mathematics achievement of primary school 8th grade students. Mersin University Journal of the Faculty of Education, 1(2), 250-260. Retrieved from http://dergipark.ulakbim.gov.tr/mersinefd/article/download/5000003018/5000003551
  • Vukovic, R.K., Kieffer, M.J., Bailey, S.P., & Harari, R.R. (2013). Mathematics anxiety in young children: Concurrent and longitudinal associations with mathematical performance. Contemporary Educational Psychology, 38(1), 1-10. http://dx.doi.org/10.1016/j.cedpsych.2012.09.001
  • Wang, X., & Cheng, L. (2010). Chinese EFL students’ perceptions of classroom assessment environment and their goal orientations. In Cheng, L. & Curtis, A. (Eds.), English language assessment and the Chinese learner (pp. 202-218), Taylor & Francis.
  • Wang, Z., Hart, S.A., Kovas, Y., Lukowski, S., Soden, B., Thompson, L.A. et al. (2014). Who is afraid of math? Two sources of genetic variance for mathematical anxiety. Journal of Child Psychology and Psychiatry, 55(9), 1056-1064. http://dx.doi.org/10.1111/jcpp.12224
  • Wannarka, R., & Ruhl, K. (2008). Seating arrangements that promote positive academic and behavioural outcomes: A review of empirical research. Support for Learning, 23(2), 89-93. http://dx.doi.org/10.1111/j.1467-9604.2008.00375.x
  • Yenilmez, K., & Ozabaci, N.S. (2003). A research on the relationship between mathematics attitudes and mathematics anxiety of teacher high school students. Pamukkale University Journal of Education, 14(2), 132-146. Retrieved from http://pauegitimdergi.pau.edu.tr/Makaleler/651870456_11-YATILI%20%c3%96%c4%9eRETMEN%20OKULU%20%c3%96%c4%9eRENC%c4%b0LER%c4%b0N%c4%b0N%20MATEMAT%c4%b0K%20%c4%b0LE%20%c4%b0LG%c4%b0L%e2%80%a6.pdf
  • Yenilmez, K., & Ozbey, N. (2006). A research on the level of mathematics anxiety of secondary school and private school students. Journal of Uludag University Faculty of Education, XIX(2), 431-448. Retrieved from http://ucmaz.home.uludag.edu.tr/PDF/egitim/htmpdf/2006-19(2)/M13.pdf
  • Young, M.R. (2005). The motivational effects of the classroom environment in facilitating self-regulated learning. Journal of Marketing Education, 27(1), 25-40. http://dx.doi.org/10.1177/0273475304273346
  • Yuen-Yee, G.C., & Watkins, D. (1994). Classroom environment and approaches to learning: An investigation of the actual and preferred perceptions of Hong Kong secondary school students. Instructional Science, 22(3), 233-246. http://dx.doi.org/10.1007/BF00892244
  • Yuksel Sahin, F. (2008). Mathematics anxiety among 4th and 5th grade Turkish elementary school students. International Electronic Journal of Mathematics Education, 3(3), 179-192. Retrieved from http://www.iejme.com/032008/d3.pdf