the diet, and whether it is a reliable measure across time and across studies. It will be difficult to evaluate the adequacy of SNAP allotments until agreement is reached on the type of diet quality index needed for this purpose.
Thus, longitudinal data on SNAP participation, food security, and dietary intake are needed. With such data, researchers could track changes in the outcomes of food security and diet quality over time and relate changes in SNAP participation to changes in these outcomes. While assessment of the adequacy of SNAP allotments may be based on examining whether program participants appear to be meeting the goals of improving food security and access to a healthy diet, it is not clear what standards should be used to determine whether food security has been sufficiently improved or whether participants truly have access to a healthy diet. For example, what level of food security among participants would be required to determine that SNAP benefits are adequate? Should SNAP benefits be expected to eliminate low and/or very low food security entirely (if both, this would imply that the resulting rate of food insecurity should be zero percent among participants for benefits to be judged adequate)? Or would a more appropriate standard be to expect the rate of low and/or very low food security to be approximately the same among participants as among low-income nonparticipants? And what standards of nutrient adequacy should be expected—perhaps an HEI-2005 score equal to that of nonparticipants?
Key to defining the adequacy of SNAP allotments is having estimates of the impact of these benefits on such outcomes as diet quality, obesity, or food security. However, self-selection into SNAP greatly complicates such estimates. Because individuals and households choose whether to participate in the program if they are eligible, the unmeasured characteristics of participants may differ in important ways from those of nonparticipants. Further, these differences in unmeasured characteristics may be related to key outcomes of interest. Thus, a difference in outcomes between participants and nonparticipants could be due either to differences in their unmeasured characteristics or to the effect of program participation. Although a number of sophisticated methods have been developed to address this challenge, none of these methods is perfect, and critics have challenged their validity.
In assessing the feasibility of defining the adequacy of SNAP allotments, the committee considered a range of evidence on the impact of SNAP program participation on achieving the program goals of improving food security and access to a healthy diet. In general, the committee found that it would be useful to conduct further research examining food security and