Taking advantage of the strengths of 2 different dietary assessment instruments to improve intake estimates for nutritional epidemiology

Abstract

With the advent of Internet-based 24-hour recall (24HR) instruments, it is now possible to envision their use in cohort studies investigating the relation between nutrition and disease. Understanding that all dietary assessment instruments are subject to measurement errors and correcting for them under the assumption that the 24HR is unbiased for usual intake, here the authors simultaneously address precision, power, and sample size under the following 3 conditions: 1) 1-12 24HRs; 2) a single calibrated food frequency questionnaire (FFQ); and 3) a combination of 24HR and FFQ data. Using data from the Eating at America's Table Study (1997-1998), the authors found that 4-6 administrations of the 24HR is optimal for most nutrients and food groups and that combined use of multiple 24HR and FFQ data sometimes provides data superior to use of either method alone, especially for foods that are not regularly consumed. For all food groups but the most rarely consumed, use of 2-4 recalls alone, with or without additional FFQ data, was superior to use of FFQ data alone. Thus, if self-administered automated 24HRs are to be used in cohort studies, 4-6 administrations of the 24HR should be considered along with administration of an FFQ.

Figure 1.

Ratio of R² to the use of the calibrated combination of 12 24-hour dietary recalls (24HRs) plus a food frequency questionnaire (FFQ), Eating at America’s Table Study, 1997–1998. The solid line shows results for calibrated 24HR(s) only. The dashed line shows results for a calibrated combination of 24HR(s) + FFQ. The dotted line shows results for the calibrated FFQ only. A) Energy-adjusted total fat intake; B) energy-adjusted vitamin C intake; C) energy-adjusted intake of whole grains; D) energy-adjusted intake of dark green vegetables. See Web Appendix 7 for plots for the other dietary components.

Figure 2.

Comparison of statistical powers (%) when the use of a calibrated combination of 12 24-hour dietary recalls (24HRs) plus a food frequency questionnaire (FFQ) leads to 90% power, Eating at America’s Table Study, 1997–1998. The solid line shows results for calibrated 24HR(s) only. The dashed line shows results for a calibrated combination of 24HR(s) + FFQ. The dotted line shows results for the calibrated FFQ only. A) Energy-adjusted total fat intake; B) energy-adjusted vitamin C intake; C) energy-adjusted intake of whole grains; D) energy-adjusted intake of dark green vegetables. See Web Appendix 7 for plots for the other dietary components.

Figure 3.

The relative sample size necessary to achieve 90% power compared with the sample size necessary to achieve 90% power using the calibrated combination of 12 24-hour dietary recalls (24HRs) plus a food frequency questionnaire (FFQ), Eating at America’s Table Study, 1997–1998. The solid line shows results for calibrated 24HR(s) only. The dashed line shows results for a calibrated combination of 24HR(s) + FFQ. The dotted line shows results for the calibrated FFQ only. The vertical axis shows the relative sample size as a percentage; for example, a value of 200 means that the relative sample size is 200% of that required when using 12 24HRs plus an FFQ. A) Energy-adjusted total fat intake; B) energy-adjusted vitamin C intake; C) energy-adjusted intake of whole grains; D) energy-adjusted intake of dark green vegetables. See Web Appendix 7 for plots for the other dietary components.