Warrantless arrest laws for domestic violence (DV) are generally classified as discretionary, preferred, or mandatory, based on the level of power accorded to police in deciding whether to arrest. However, there is a lack of consensus in the literature regarding how each state's law should be categorized. Using three classification schemes, this study examined whether variations among these schemes impact research outcomes by analyzing the effects of discretionary, preferred, and mandatory warrantless arrest laws on intimate partner homicide (IPH). Variations in classification schemes and in the dates of law passage presented in the literature resulted in differing estimated effects of the laws. (Contains 4 tables and 1 note.)