Variability in Selected Indexes of Overall Diet Quality

We examined the intra- and interindividual variability in selected measures of overall diet quality in relation to socio-demographic, lifestyle, and health-related characteristics. Three days of dietary data from the Continuing Survey of Food Intakes by Individuals (CSFII), 1989–91 (7841 respondents, 3337 men and 4504 women, aged ≥ 19 years), were examined. Measures of overall diet quality were: 1. the Dietary Diversity Score (DDS), a measure of variety among the major food groups; 2. the Overall Variety Score (OVS), examined the number of nutrient-dense foods reported; and 3. the Nutrient Adequacy Score (NAS100), evaluated the number of nutrients consumed at least at the level of the RDA from a total of 11. The ratio of intra- to interindividual variance for DDS, OVS, and NAS100 was 1.66, 1.09, and 1.21, respectively, indicating higher intraindividual variability relative to interindividual variability. For each of the three scores, gender, income, education, and smoking were associated with greater intraindividual variability; however, age, and special diet status were associated with lower variability. Thus, the reliability of a given dietary assessment protocol for evaluating “usual” diet quality is likely to vary by the socio-demographic and lifestyle characteristics of the study population.