Evaluation of alternative approaches to assign nutrient values to food groups in food frequency questionnaires

Although every food frequency questionnaire (FFQ) requires a nutrient datab ase to produce nutrient intake estimates, it is often unclear how a particu lar database has been generated. Moreover, alternative methods for construc ting a database have not been rigorously evaluated. Using 24-hour recalls f rom the 1994-1996 Continuing Survey of Food Intake by Individuals, the auth ors categorized 5,261 individual foods reported by 10,019 adults into 170 f ood groups consistent with line items on an FFQ. These food groups were use d to generate 10 potential nutrient databases for a FFQ that varied by whet her the authors 1) used means or medians, 2) did or did not consider age, 3 ) incorporated collapsing strategies for small age-gender-portion size cell s, 4) excluded outliers in a regression, and 5) used weighted median nutrie nt density x age-gender-portion size-specific median gram weights (Block me thod). Mean error, mean squared error, and mean absolute error were calcula ted and compared across methods, with error being the difference in total o bserved (from recalls for each individual) and total estimated intake (from each of the 10 methods) for seven nutrients. Mean method's for assigning n utrients to food groups were superior to median approaches for all measurem ents. Among the mean methods, no single variation was consistently better.