ABSTRACT
Ecological studies are based on grouped data, with the groups in a spatial context corresponding to geographical areas. In addition to epidemiology and public health [1], ecological studies have a long history in many disciplines, including political science [2], geography [3], and sociology [4]. Due to aggregation, ecological studies are susceptible to unique challenges, in particular the potential for ecological bias, which is the difference between estimated associations based on ecological-and individual-level data.
