本文的目的，在於瞭解影響預測市場準確度的因素。我們使用未來事件交易所2008－2010年的選舉交易資料，分析影響預測市場準確度的原因。實證結果發現，預測困難度、市場交易特徵及邊際交易者比例都會影響預測結果的準確度，此結果不因控制選舉類別、政黨屬性或選舉區域等變數而有不同。值得注意的是，本文藉由台灣選舉預測市場的資料，明確地說明預測市場之所以準確的理由，其中邊際交易者是影響預測準確度的最關鍵因素。本研究的理論意涵為：邊際交易者為該合約全部交易者中的最佳交易者，即使其人數有限，亦能將正確的消息透過市場價格反映出來，並提高預測市場的準確度。 This paper seeks to uncover the factors associated with the accuracy of prediction markets. We used the 2008-2010 Taiwan election trading data obtained from the Exchange of Future Events to study the accuracy of the prediction market. Our empirical analysis shows that, after controlling for election types, political parties, and electoral districts, the accuracy of prediction market is affected by the difficulty of prediction, the characteristics of market trading, the degree of market consensus, and the percentage of marginal traders. Our study of Taiwan's prediction market data shows clearly that ＂marginal traders＂ is the best predictor of the accuracy of the prediction market. Accordingly, this paper has the following theoretical implications: marginal traders, defined as the most successful traders, can disclose the most accurate information concerning the potential candidates, and may have the means to form market consensus even if they are limited in number.