The evidence supporting the substance abuse prevention strategies in the literature varies widely. These differences do not always mean that one strategy is intrinsically better than another. They may reflect the fact that some strategies have not been as thoroughly studied as others or have not been evaluated for application to college drinkers. To provide a useful list that accounts for the lack of research as well as negative findings, Task Force members placed prevention strategies in descending tiers on the basis of the evidence available to support or refute them.