A deeper look at interstate war data: Interstate War Data version 1.1

This paper accomplishes two related goals. Firstly, it presents version 1.1 of the Interstate War Data (IWD) data set. IWD is a data set of all interstate wars, using Correlates of War (COW) rules but improving on COW by repairing the high number of coding errors in COW and more accurately and precisely treating multilateral wars. IWD 1.1 makes important improvements over IWD 1.0, such as describing interstate wars and war participants previously neglected by COW and IWD 1.0 and extending the temporal range forward to 2013. It also is the first data set to provide a systematic list of all interstate wars back to 1816 with at least 500 battle deaths (COW and IWD 1.0 only listed those conflicts with at least 1000 battle deaths). Secondly, the paper discusses important issues in collecting data on interstate wars, especially collecting reliable data on battle dead. Battle dead data are critical both for constructing data sets and for testing hypotheses, but frequently battle dead estimates vary widely, and come from sources of varying quality. The paper discusses the importance of using reliable sources, and in particular of minimizing reliance on military encyclopedias