According to Dunn 2012, public variables include level of educational opportunity, degree of public safety, and air quality. One difficulty with public policy analysis is that frequently we do not have precise definitions of these public variables. It's best that to think about two kinds of definitions of variables: constitutive and operational. Constitutive definitions give meaning to variables by using other synonymous words. For example, educational opportunity may be constitutively defined as "the freedom of chose learning environments consistent with one's abilities." Such definitions, although essential, provide us with no concrete rules or guidelines for actually