The NPC study was designed to overcome some of the methodological limitations of past studies of the benefits and costs of drug and/or alcohol treatment. The research design was created with a representative sample of treatment completers with a matched comparison group of clients who received little or no treatment; use of existing state agency databases rather than self-report data for maximum objectivity; and an adequate study period of 2 years prior and 3 years subsequent to treatment completion. The study results indicated that successful drug and alcohol treatment can have positive societal outcomes. While previous studies have shown the positive effects of treatment for the time period of 1 year, this study indicated that these gains are sustained over longer periods of time (up to 3 years). The study estimated the cost savings to taxpayers — either directly in their avoidance of criminal losses or indirectly in the avoidance of expenditure of their tax dollars — that accrue from the positive societal outcomes of treatment.