應用PBM 模型在臺灣魚市場整合之研究

Market Integration in Taiwan’s Aquaculture Markets ─ An Application of the PBM model

本研究主要在應用新近發展的等值臨界模型 (Parity Bounds Model) 對臺北、臺中兩地魚市場中，都有進行交易之七星鱸、大頭鰱、草魚、虱目魚、鯉魚、鯽魚、白口、肉魚、黑鯧、白鯧、金線等十一種魚種進行市場整合檢定，並與另一種市場整合檢定－－Ravallion 模型比較，希望藉此二種不同方法來了解臺北、臺中兩地魚市場間是否符合單一價格法則所隱含之市場整合的情形。比較Ravallion 模型及等值臨界模型方法可知，Ravallion模型並未考慮轉運成本 (transfer cost)，可能產生過度拒絕市場整合檢定之結果。而等值臨界模型則考慮轉運成本因素，利用常態分配求取價差小於、等於、大於轉運成本等三種市場整合情況之機率值。與Ravallion 模型檢定之只有拒絕或接受兩種兩極化結果相比，應更能說明市場間不同的整合情況。根據本研究實證結果顯示，臺北、臺中魚市場間之各魚種市場整合程度都還算高；我們也發現大部份養殖魚類市場整合程度較冰藏魚類為低，顯示養殖魚類運銷體系仍有改善空間。

The main purpose of this article is to apply the newly developedParity Bounds model and then compare it with Ravallion model in themarket integration research of Taipei and Taichung aquaculture markets.We choose 11 types of fishes including Japanese seaperch, big headcarp, milk fish, grass carp, common carp, curcian carp, white mouthcroaker, Japanese butterfish, black pomfret, white pomfret, and goldthreadfin. Our results show that without taking transfer costs into account,Ravallion model tends to over-reject the market integration hypothesis.Using three regimes to explain the relationship between price differencesand transfer cost, Parity Bounds Model seemingly works better ascompared to Ravallion model, which uses only two hypotheses to testmarket integration. We found that most of fishes boast high-degree ofmarket integration. In addition, the degree of market integration forcultured fishes is lower than that for cold storaged fishes, that means themarketing system for cultured fishes should improve.