集體購物是動態定價的一個應用，而集體購物本身是一個允許消費者透過聚集數量來獲得折扣的機制。在集體購物中，價格取決於所累積的數量。而集體購物中給予的價格曲線會呈現當前的累積訂單數量及價格，消費者將可能對未來的價格產生一些價值的期望與不確定性。
過去文獻透過網路上實際資料的整理，提出參與外部性效應及降價效應這兩現象出現在集體購物中(Kauffman and Wang, 2001;2002)。因為過去研究沒有透過變數的控制而提出兩個現象，我們無法真正了解到底是哪些因素影響兩個現象的形成。因此，本研究將透過實驗法來了解兩現象的存在性及其成因。本研究目的為探究是否參與外部性效應及降價效應存在於集體購物中並探究知覺風險與知覺價值是否與兩現象有相關，進而了解消費者加入集體購物的意圖是否受到知覺風險與知覺價值的影響。
本研究結果顯示外部性效應及降價效應確實存在於集體購物中。而外部性效應是由於消費者的財務風險、時間風險及知覺價值所產生；降價效應則受到財務風險而形成。此外，當消費者有愈低的知覺風險及愈高的知覺價值，加入集體購物的意圖就會愈高。

Group buying is one dynamic pricing application and it is a mechanism permitting consumers to gather bargaining power in order to get a volume discount or other premiums. In group-buying, the price depends on the number of collected orders. Given a price curve shows the existing orders and current price, the consumer will have some expectation of value and uncertainty for future price.
Previous literatures found both the positive participation externality effect and price-drop effect from the field data (Kauffman and Wang, 2001; 2002). Because there are no variable controls from the field study, we can not really know what reasons cause these phenomena in group-buying. Thus, this study will use experimental methodology to the existence of these two effects and understand why they happen. The purpose of this research is to investigate whether positive participation externality effect and price-drop effect exists in group-buying and to explore whether the two effects are related to consumers’ perceived risk and perceived value, whether the intention to join group-buying is influenced by perceived risk and perceived value.
The study shows that the two effects really happen in group-buying. Participation externality effect is caused by financial risk, time risk and perceived value. However, price-drop effect is generated from financial risk. Additionally, consumers have higher intentions to join group-buying when they perceive lower financial risk and more perceived value.

Chapter1. Introduction 1
1.1 Online Group-Buying – A Beneficial Business Model in EC 1
1.2 Research Motivation and Purpose 2
Chapter2. Literature Review 5
2.1 Online Group-Buying 5
2.1.1 Online Group Buying Model 5
2.1.2 Buyer Behavior in Group Buying 5
2.2 Perceived Risk 7
2.2.1 The Definition of Risk 7
2.2.2 Concept of Perceived Risk 8
2.2.3 Consumers’ Perceived Risk and Risk Attitude in Group Buying 9
2.3 Price, Quality, and Value Perception 11
2.3.1 The Concept of Price 11
2.3.2 The Concept of Perceived Sacrifice 12
2.3.3 The Concept of Perceived Quality 12
2.3.4 The Concept of Perceived Value 12
Chapter3. Research Model and Hypotheses 15
3.1 Research Model 15
3.2 Hypotheses 17
3.2.1 Price Level and Perceived Risks 17
3.2.2 Price Level and Perceived Values 18
3.2.3 Different Timing and Perceived Risks 18
3.2.4 Different Timing and Perceived Values 19
3.2.5 Perceived Risks and Intention to Join Group-Buying 19
3.2.6 Perceived Values and Intention to Join Group-Buying 20
Chapter4. The Experimental Approach 21
4.1 Experimental Design 21
4.2 Subjects and Implementation 23
4.2.1 Subjects 23
4.2.2 Implementation 23
4.3 Measurements 25
Chapter5. Analysis and Result 29
5.1 Descriptive Statistics 29
5.2 Measurement validity and reliability 30
5.3 Hypotheses Testing 32
5.4 Discussion 40
5.4.1 Participation Externality Effect Test 40
5.4.2 Price-Drop Effect Test 40
5.4.3 Perceived Risk, Value and Intention to Join 40
Chapter 6. Conclusion 42
6.1 Contribution and Applications 42
6.2 Limitation 42
6.3 Future Research 43
References 44
Appendix A: Questionnaires 47
Appendix B: Group-Buying System 53

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