| Acknowledgement | 第1-6页 |
| 摘要 | 第6-8页 |
| Abstract | 第8-12页 |
| Chapter Ⅰ Introduction | 第12-18页 |
| ·Why not party unity scores: the invisible defection and vote-specific variance | 第13-15页 |
| ·Significance of the study | 第15-18页 |
| Chapter Ⅱ Literature Review | 第18-32页 |
| ·Party unity: conceptualization and measurement | 第18-21页 |
| ·Party unity: the game between collective and individual preferences | 第18页 |
| ·Measuring party unity with roll call data | 第18-21页 |
| ·Explaing variation in party unity: competingpressures and differing goals | 第21-29页 |
| ·Theories of congressional organization: the partisan and the party-less | 第22-26页 |
| ·Explaining party unity: both collective and individual preferences matter | 第26-29页 |
| ·A brief introduction to the research design | 第29-32页 |
| Chapter Ⅲ Theoretical Framework | 第32-71页 |
| ·The game between collective and ividual preferences: an overall framework | 第32-35页 |
| ·Conditional procedural-unity-oriented voting theory: cofe-type and party unity | 第35-50页 |
| ·Legislative proceedings and the three types of votes | 第35-38页 |
| ·Vote-type and party unity | 第38-44页 |
| ·Hypotheses | 第44-50页 |
| ·Condinonal presidential-position-oriented cross-voting theory: presidential pubic position and party unity | 第50-63页 |
| ·Executive influence in the legislative arena | 第50-52页 |
| ·Supporting presidential positions: a congressional perspective | 第52-58页 |
| ·Hypotheses | 第58-63页 |
| ·System-level factors and party unity | 第63-69页 |
| ·The postreform House,party polarization and party unity | 第63-69页 |
| ·Congressional election years and party unity | 第69页 |
| ·Summary of the theoretical framework | 第69-71页 |
| Chapter Ⅳ Research Design: Measurement and Data | 第71-77页 |
| ·Party unity | 第72页 |
| ·Vote-type | 第72-73页 |
| ·Presidential position taking | 第73-74页 |
| ·Postreform polarization | 第74-75页 |
| ·Congressional election years | 第75-76页 |
| ·Model equetion and estimation technique | 第76-77页 |
| Chapter Ⅴ Regression Models: Results and Discussion | 第77-87页 |
| ·Assessing the theory of conditional procedural-unity-oriented voting | 第77-80页 |
| ·Assessing the theory of conditional presidential-position-oriented cross-voting | 第80-82页 |
| ·Postreform House,polarization and congressional election years | 第82-87页 |
| Chapter Ⅵ Conclusion | 第87-92页 |
| ·Limitations and direction for future research | 第90-92页 |
| Works Cited | 第92-100页 |
| Appendix A. Vote Categorization | 第100-101页 |
