The USDA Healthy Eating Index-2005 (HEI-2005) is a tool to quantify and evaluate the quality of diet consumed by the U.S. population. It comprises 12 components, expressed as ratios of a food group or nutrient to energy intake. The components are scored on a scale from 0 to M, where M is 5, 10, or 20. Ideally, the HEI-2005 is calculated on the basis of the usual dietary intake of an individual. Intake data, collected via a 24-h recall, are often available for only 1 d for each individual. In this article, we examine how best to estimate a population's mean usual HEI-2005 component and total scores when 1 d of dietary information is available for a sample of individuals from the population. Three methods are considered: the mean of individual scores, the score of the mean of individual ratios, and the score of the ratio of total food group or nutrient intake to total energy intake, which we call the population ratio. We investigate via computer simulation which method is the least biased. The simulations are based on statistical modeling of the distributions of intakes reported by 738 women participating in the Eating at America's Table Study. The results show that overall, the score of the population ratio is the preferred method. We therefore recommend that the quality of the U.S. population's diet be assessed and monitored using this method.