A Comparison of Self-Organizing Maps and Pathfinder Networks for the Mapping of Co-Cited Authors A Thesis Submitted to the Faculty of Drexel University by Jan William Buzydlowski in partial fulfillment of the requirements for the degree of Doctor of Philosophy December 2002 © Copyright 2003 Jan William Buzydlowski. All Rights Reserved ii Dedications To my father. iii Acknowledgements Howard D. White, PhD, thesis advisor, who never treated me as a student, but from whom I learned more than any other teacher. The distinguished members of my committee: · Xia Lin, PhD, who treated me as a colleague and friend. · Katherine W. McCain, PhD, who always knew what to do. · Richard Heiberger, PhD, who showed me fascinating new worlds. · Stephen Kimbrough, PhD, for his invaluable contribution. J. Jeffery Hand, Linda Marion, Joan Lussky for their camaraderie. All of the experts involved with this study who were more than generous with their time and expertise. Cheryl L. Berringer for her emotional support, without which none of this would have been possible. iv Table of Contents List of Tables ......................................................................................................... vii List of Figures ........................................................................................................viii Abstract ....................................................................................................................x 1. INTRODUCTION AND STATEMENT OF PROBLEM ...................................1 1.1. Goal of the Research.............................................................................1 1.2. Research Questions...............................................................................4 1.3. Context of the Research........................................................................7 1.4. Interpreting AuthorLink Maps: An Example......................................13 1.5. Setting the Stage.................................................................................17 2. RELEVANT LITERATURE.............................................................................19 3. PATHFINDER NETWORKS ...........................................................................26 3.1. Computing Pathfinder Networks ........................................................26 3.2. Displaying Pathfinder Networks.........................................................30 4. SELF-ORGANIZING MAPS............................................................................34 4.1. Computing Self-Organizing Maps......................................................34 4.2. Displaying Self-Organizing Maps ......................................................38 5. METHODOLOGY.............................................................................................40 5.1. Overview.............................................................................................40 5.1.1 Data .......................................................................................40 5.1.2. The Computer System Used to Generate the Maps .............42 5.2. Procedure ............................................................................................44 5.2.1. Selecting the Experts............................................................45 v 5.2.2. Selecting Author Names Used for the Experiment ..............46 5.2.3. Extracting the Experts’ Mental Maps ..................................48 5.2.4. Creating a Data Structure to Represent the Groupings........51 5.2.5. Determining the Groupings that Exist on Generated Visual Maps .........................................................................53 5.2.6. Combining the Co-Membership Matrices ...........................59 5.3. Research Questions.............................................................................60 5.3.1. Research Question 1.............................................................61 5.3.2. Research Question 2.............................................................64 5.3.3. Research Question 3.............................................................70 6. RESULTS ..........................................................................................................72 6.1. Research Question 1............................................................................72 6.2. Research Question 2............................................................................74 6.3. Research Question 3............................................................................78 6.3.1. Effects of Demographics......................................................80 7. SUMMARY OF INTERVIEWS .......................................................................84 8. THE EXPERTS’ COMPOSITE MAP OF PLATO...........................................90 9. FINAL SUMMARY AND FUTURE WORK...................................................99 9.1. Database Development .....................................................................100 9.2. Enrichment of PFNETs.....................................................................102 9.3. Further Improvement of AuthorLink ................................................103 BIBLIOGRAPHY................................................................................................106 APPENDIX A: SOURCE AND DERIVED DATA............................................112 vi APPENDIX B: A CO-OCCURRENCE CALCULUS ........................................115 APPENDIX C: THE EXPERTS’ AREAS OF EXPERTISE AND NAMESEEDS ...................................................................119 APPENDIX D: INTRODUCTORY LETTER ....................................................120 APPENDIX E: INSTRUCTIONS TO EXPERT.................................................122 APPENDIX F: AFFILIATION OF EXPERTS ...................................................125 APPENDIX G: DATA FROM EXPERTS ..........................................................126 APPENDIX H: EXPLANATION OF THE SYSTEM ........................................186 APPENDIX I: THE INTERVIEW QUESTIONS...............................................189 APPENDIX J: INTERVIEW EXAMPLE ...........................................................191 APPENDIX K: ACCUMULATED MATRICES BASED ON PLATO .............204 APPENDIX L: MAP PREFERENCES OF EXPERTS .......................................207 APPENDIX M: AUTHORS ASSOCIATED WITH THE INTEREST NAMESEEDS............................................................................210 Vita.......................................................................................................................217 vii List of Tables 1. 24 Authors Associated with Plato....................................................................47 2. Grouping Statistics for the Card Sorts .............................................................50 3. A Possible Grouping of the 25 Authors Associated with Plato .......................51 4. A Possible Grouping of the 25 Authors Associated with Plato .......................53 5. Example of a Card Sort....................................................................................58 6. Two Abridged Co-Membership Matrices........................................................66 7. Scoring the Difference of Two Vectors ...........................................................67 8. Fictitious Scores of 5 Experts ..........................................................................68 9. QAP Correlation between SOM Circling and Card Sort .................................73 10. QAP Correlation between PFNET Circling and Card Sort .............................73 11. Co-membership Agreement Measures and Average .......................................75 12. Results of the t-test...........................................................................................76 13. Distribution of Map Preference........................................................................79 14. Counts of Area of Expertise by Map Preference .............................................80 15. Statistics of Area of Expertise by Map Preference ..........................................81 16. Counts of Gender by Map Preference..............................................................81 17. Statistics of Gender by Map Preference...........................................................82 18. Counts of Institutional Affiliation by Map Preference ....................................82 19. Statistics of Institution by Map Preference......................................................83 20. 24 Associated Authors with Plato....................................................................90 21. Accumulated Parings by Experts .....................................................................92 viii List of Figures 1. Initial AuthorLink Screen..................................................................................8 2. Authors with Counts ..........................................................................................9 3. SOM of Plato ...................................................................................................10 4. PFNET of Plato................................................................................................11 5. Retrieved Articles ............................................................................................12 6. SOM of Descartes ............................................................................................14 7. PFNET of Descartes.........................................................................................15