In addition to their clear relevance to public health, MLDA policies are attractive to study because changes in MLDA policies occurred in different states at different time periods, enabling quasi-experimental comparisons of state-by-state differences in MLDA. There have been two waves of change in the MLDA policy environment. The first occurred in the early 1970s, when drinking age laws were being liberalized in conjunction with broader social change. After several years of relative stability, a second wave of change occurred throughout the 1980s, when drinking ages were raised as a public health measure (Toomey et al, 1996).
