從合作興築埤圳所要進行的活動為出發點，我們以五個可被交易雙方及分析者共同 觀察的客觀因素來討論興築方式的選擇，並得出影響契約選擇的五個假設。實證的結果顯示， 在影響眾農合築與請埤圳主興築兩種契約選擇的因素中，較顯著的是灌溉面積和水源。灌溉 面積影響埤圳組織的運作成本和水租的收集成本；水源則影響興築埤圳的資金募集成本。不 論是無限長期的請圳主契約或垂直整合眾農合築，我們的研究結論是：在清朝宜蘭的埤圳興 築裡，主觀交易成本理論不僅可以解釋其中的契約選擇，還可提供一個臺灣早期經濟得以順 利發展的解釋。

　　　　　With the subjective transaction cost theory, we derive five hypotheses about contractual choices in the construction of an irrigation system. From the activities that need to be taken to complete an irrigation system, we obtain five objective variables to test our hypotheses. Our empirical result shows that, in the choices of farmer-collective and entrepreneur-inviting construction, the irrigation area and the water source have signification influences. The irrigation area influences the organizational cost of the irrigation system: the water source influences the financing cost for construction. For both the permanent entrepreneur-inviting and vertically integrated farmer-collective contracts, our conclusion is: The subjective transaction cost theory can explain not only the contractual choices on the Lan-Yang Plain, but also the successful economic development of Taiwan in Tsing Dynasty.