台灣漁產品需求體系-一般化動態模型之應用

Abstract

由於漁產品消費需求結構改變，可能影響漁民收益之利弊，本研究著重近年來消費需求量價結構關係之實證估計與模擬，以確認消費需求結構改變可能之因應政策措施。利用1979年第一季至1999年第四季各主要漁產品的季別資料，建立直接需求體系(ordinary demand system)及逆需求體系(inverse demand system)之一般化模型，以Davidson-Mackinnon修正非嵌套檢定(nonnested tests)、Durbin-Wu-Hausman 檢定及RMSE比值、Theil’s U統計值預測績效指標，來檢定上述兩種一般化需求體系模型，何者最適用於台灣漁產品消費需求。接著就所選擇之需求體系予以動態化，加入對稱性及齊次性等參數限制條件，再以近似無關迴歸(SUR)方法聯立推估彈性，作為分析基礎，並研擬可能改善漁民收益之具體建議。依實證結果可歸納出以下幾點重要結論： (一)、經由Davidson-Mackinnon修正非嵌套(non nest)檢定、Hausman檢定及RMSE比值及Theil’s U統計值預測績效指標發現，台灣地區漁產品需求體系「以價格內生之一般化逆需求體系」較為適合；而模型的選擇以組合模型(一般化模型)為最合適。 (二)、動態行為的調整係數λ在模型中具有相當高的顯著水準，表示漁產品的消費支出無法隨著當期規模及數量的變動迅速調整，會受到過去消費習慣及前期漁產品本身數量及規模影響，使短期的消費支出無法立即調整至最適。所以業者應依據這種需求行為的僵固性來促銷，如配合重要傳統節日，如清明節、端午節、中元節及春節等來促銷。 (三)、所有漁產品自身數量彈性小於一，但數量增減對漁民收益的影響仍需依漁產品量價關係而定。吳郭魚、虱目魚、蝦類、鯧魚、鯛魚及比目魚未受補償自身數量彈性達到統計上的顯著性水準，以鯧魚未受補償自身數量彈性最大為-0.344，比目魚最小為-0.024。漁產品自身數量彈性不具彈性，隱含過去政府對漁產品產銷調節，達到價格穩定與保障漁民利益有其成效，今後隨著漁產品市場開放後，漁產品價格穩定政策，勢必持續進行以保障漁民收益。 (四)、本研究漁產品所推估自身數量彈性不具彈性，表示消費需求量與漁民收益是同向變動，所以漁產品消費數量的增加，才能有助於漁民收益增加。部分沿近海與遠洋魚類如鯛魚、鯧魚及鰆旗魚呈現消費需求量增加較為明顯，且價格呈現上漲，對該類漁民收益有利。養殖虱目魚、貝類及遠洋鮪魚呈現消費數量增加且價格呈現下跌，在該類漁產品自身數量彈性缺乏彈性或無彈性時，隨著消費數量增加會使虱目魚、貝類養殖漁民及遠洋鮪魚捕撈漁民收益有利。養殖蝦類呈現消費數量減少且價格呈現上漲，在蝦類自身數量彈性缺乏彈性時，隨著消費數量減少會使蝦類養殖漁民收益減少。養殖吳郭魚及沿近海白帶魚及花枝，呈現消費數量減少且價格呈現下跌，其無法出口競爭的吳郭魚養殖業者及白帶魚、花枝捕撈者收益將惡化。

The structural changes in the consuming demand of fishery products may have the possibility to affect the revenue of the fishermen. This study would like to emphasize the actual estimate and model of the structural relationship between the quantity and price of the consumer demand occurred in the recent year, so as to ensure the policy to be effected by the government according to the structural changes of the consumer demand. The generalized models of both Ordinary Demand System and Inverse Demand System were been set up by the uses of the quarterly information of major fishery products from the first quarter of 1979 throughout the fourth quarter of 1999. Then, these two generalized models of demand systems were been testified to determine which one of them is suitable for the consumer demand of fishery products in Taiwan through the modified nonnest tests of Davidson-Mackinnon , Durbin-Wu-Hausman tests, and the forecasting performance by RMSE Ratio and Theil’s U-Statistics as well. Added with the restrictions imposed by symmetry and homogeneity , and then followed with the method of SUR for the estimated flexibilities, the selected demand system incorporate dynamic specifications as the basis of analysis, and to complete some constructive recommendation, which will improve and promote the revenue of the fishermen. And the following conclusions were resulted through the actual tests. 1. It is concluded that “The generalized inverse demand system with prices dependent on quantities” seemed to be suitable for the demand system of fishery products in Taiwan, throughout the tests by the Davidson -Mackinnon modified nonnested tests, Durbin-Wu-Hausman tests, and the forecasting performance by RMSE Ratio and Theil’s U-Statistics as well. Also, the synethic model (generalized model) seemed to be in the most suitable use for Taiwan. 2. The adjusting coefficient “λ”of dynamic behavior is highly significant level within the model. This appeared that the consuming expenditure to the fishery products would not be rapidly adjusted according to the current but to the previous changes in both the scale and the quantities. This has made that the short-term consuming expenditure couldn’t be re-adjusted to its optimum level in time. Therefore, the marketing programs should be made incorporation with some festival activities in the traditional holidays, e.g., Ching-Ming Festival (清明節), Dragon Boat Racing Festival (端午節), Ghost Festival (中元節), and Chinese New Year Holiday, etc. under such a rigid consuming tendency. 3. The own-price flexibilities of all the fishery products are less then one (1). However, the effects of the increase or decrease in quantity to the fishermen’s revenue is still depending on the relation between the quantity and price of the products themselves. The uncompensated own-price flexibilities of tilapia, milkfish, shrimps, pornfret, sea bream, and cod are statistically significant at the 15% level. The pornfret had the highest flexibility at —0.344, whilst the cod had the lowest flexibility at —0.024 among them. The own-price inflexibility of the fishery products themselves indicated that the government had well safeguarded the fishermen’s profit and well kept the prices stable through the efficient policies effected in the past time. The policy of stable pricing must be continued in order to well protect the fishermen’s revenue under the coming policy of totally opening the imports of fishery products from the worldwide countries. 4. The nature of the own-price inflexibility of the fishery products themselves as concluded throughout this study indicated that both the quantity of consumer demand and the revenue of the fishermen are proceeding in parallel. The fishermen’s revenue can be increased only by the increase of the quantity demanded. The apparent increase in both the quantity demanded and the price of the offshore & coastal and far sea fishery, like sea bream, pornfret, mackerel and marlin, had been proved good to the revenue of the fishermen. For the milkfish、shellfishes of the aquaculture, and the tuna of the far sea, it appeared that the quantity demanded was going up, whilst the prices were getting down. When the own-price inflexilibities or even non-flexilibities, the increase in the quantity demanded will be good to the revenue of fishermen, who are in the businesses of the milkfish、shellfishes of the aquaculture, and the tuna of the far sea. It appeared that the price was going up when the quantity demanded was decreased with regards to the shrimps of aquaculture. When the shrimps’ own-price flexibility is inflexible, the decrease in the quantity demanded made the fishermen’s revenue less. With regard to the tilapia of aquaculture and the hairtail、squids of the offshore and coastal, it appeared that both the quantity demanded and price were decreased. This had made the inability of export competition for the fishermen of tilapia of the aquaculture, and made the revenue of the fishermen of hairtail and squids even worse.