Although these three studies have been used by the federal government and other entities to understand the impact of the NAP program's benefits, the data used by the authors dates back to the periods between 1977 and 1984, providing limited relevant information for the current program of today.[63] Additionally, subsequent research and analysis have revealed insufficiencies in the methodology applied by the authors of all three publications, thereby casting doubt on whether a definitive conclusion of the program's overall impact has been established.[64] A 2004 report published by USDA's Economic Research Service evaluated the reliability and relevancy of these studies, concluding that they are not sufficient to determine the program's current impact and performance, and stating:[64]