「制度相似效果」或「選擇效果」？再探民主和平論中「政治制度相似性」與「軍事衝突發生機率」之間的關係

“Institutional Similarity Effect” or “Selection Effect”? Revisiting the Relationship between “Political Institution Similarity” and “Militarized Interstate Disputes” in Democratic Peace Effects

「制度相似效果」和「選擇效果」都是「民主和平論」的重要因果機制，但支持前者的文獻在制度測量上和研究設計上普遍都有無法分離「制度相似效果」和「選擇效果」的問題，因此「制度相似效果」是否存在仍具有爭議。本文使用數種不同的政治制度分類方法，以及能夠區別兩種不同效果的研究設計，重新檢證兩國「政治制度的相似性」與「發生軍事衝突的機率」之間的關係。來自全球154國涵蓋1950～2008年的資料顯示，是雙方在民主程度上的差距所帶來的「選擇效果」，而不是雙方政治制度相似而導致利益相似的「制度相似效果」，更可能是民主和平論的主因。

Both the “institutional similarity effect” and “selection effect” are regarded as important democratic peace causal mechanisms in literature. However, the literature that supports the former effect is not able to separate these two effects in the measurement and research designs used. Therefore, whether the “institutional similarity effect” exists is still a debatable issue. In this research, I use several different measurements to conceptualize states’ political institution similarity in each dyad and apply a research design that can separate these two different effects, to re-investigate the relationship between “political institution similarity” and “militarized interstate disputes.” Empirical evidence of 154 countries from 1950 to 2008 shows that it is the “selection effect” (brought by the discrepancies between both sides’ levels of democracy), rather than the “political institution similarity effect” (resulting from the similarity in their interests caused by the similarity of their political institutions), that more likely leads to democratic peace.