本文使用2000年和2004年總統選舉各鄉鎮的投票資料，配合2000年戶口普查的人口資料，探討2004年總統選舉廢票大量增加的原因。首先，廢票比例增加較多的是都市化程度較低的縣分；民進黨主政與否，廢票比例增加的幅度並沒有明顯的差異。其次，不識字比例較高的鄉鎮，在無效票範圍擴大之後，廢票比例顯顯著地多增加了1.392%；迴歸分析結果顯示，不識字比例增加1%，會使得廢票比例多增加0.21%。區位推論模型的估計結果亦發現，不識字選民投出廢票的比例在2004年大幅增加，且明顯較識字選民高出許多。此外，我們也檢驗「做票說」對於「陳呂得票率越高，廢票比例越高」這個現象的詮釋，說明兩者並沒有因果關係。控制不識字比例之後，陳呂得票率越高的鄉鎮，其廢票比例反而是減少的，但不具統計顯著性。綜合而言，「無效票範圍擴大」是唯一與資料一致的假說。

Using data from 2000 and 2004 presidential elections and data from the 2000 population Census, this paper tests the hypotheses regarding the dramatic increase of invalid votes in 2004. First, the less-urbanized counties showed a greater increase in the proportion of invalid votes, and whether the DDP is the county ruling party does not show any significant differences. Second, as the definition of invalid votes became broader in 2004, townships with an above-median proportion of illiterate voters significantly increase dir the proportion of invalid votes by 1.392%. Regression results show that for a 1% increase in the illiteracy rate, the proportion of invalid votes increases by 0.21%. Estimation from King’s ecological inference model also shows that the probability of casting invalid votes for illiterate voters increases significantly in 2004 and is of vote-rigging based on the observation that the share of votes gathered by Chen-Lu and the proportion of invalid votes are positively correlated. It is shown that this correlation is not causal. After controlling for the illiteracy rate, the effect of the share votes gathered by Chen-Lu on the proportion of invalid votes is reversed and becomes negative, although not statistically significant. In sum, the hypothesis that invalid votes are caused by the broader definition of invalid votes is the only hypothesis consistent with the data.