The errors associated with measuring the number of militia and patriot groups may cast doubt on conclusions drawn from prior studies of the spatial variation of these movements. Most studies of militias have been qualitative investigations of a single group, state, or region. A growing number of studies, however, have used quantitative techniques to assess the hypothesis that the number of militia groups by state covaries with structural and cultural forces. We outline a number of concerns with the validity of the counts, conducted by the Anti-Defamation League and the Southern Poverty Law Center, used by these studies. We re-estimate models from previous studies using the four alternative measures of these groups employed in prior studies. We find that many inferences drawn for identical theoretical models differ based upon the measure used. These discrepancies apply not simply to tangential control variables but to indicators of key theoretical constructs. In other words, the decision as to whether or not a particular theoretical framework receives empirical support often depends upon which measure of the dependent variable is used. This suggests that the inconsistent findings in prior research may be due to measurement error and makes it difficult to assess the validity of the conclusions drawn from these studies. It is important to be aware of these weaknesses since scholars studying political crimes and related phenomena often use information from similar sources, making this specific example relevant to a more general area of research.