Using the overdispersed exponential family to estimate the distribution ofusual daily intakes of people aged between 18 and 28 in Taiwan

Assessment of usual dietary intake of a population is essential to understa nd the nutrition status of the population. Methods like 24-hour dietary rec all and food records are commonly used for this task. However, within-indiv idual variation exists in the food record data. Methods considering measure ment errors have been used to evaluate the association between nutrient int akes and diseases. Few have been devoted to estimating the distribution of usual daily intakes. This paper proposes applying the formulation of the ov erdispersed exponential family to estimate the distribution of usual nutrie nt intake and applies the adjustments developed by Liu to reduce the varian ce of the distribution. The proposed method has the advantages of working o n the original scale of data and implementation convenience. The adjustment of the variance is carried out by dividing the variance into within-indivi dual variance and among-individual variance. The adjusted variance, then, i s used to estimate the distribution of the usual daily intake. Sampling wei ghts are considered in all the steps, except the estimation of the ratio of within to among variance. The data for this study are from the Nutritional and Health Survey in Taiwan conducted between 1993 and 1996 (NAHSIT, 1993- 1996). An independent external set of data for people aged between 18 and 2 8 years (49 males and 20 females) is used to estimate the ratio of within t o among individual variance. Due to the availability of data in estimating the ratio of within to among individual variance, 430 males and 422 females in the NAHSIT sample are used to estimate the distribution of usual daily intakes for people aged between 18 and 28 in Taiwan. The distribution also allows us to estimate the proportion of people who do not meet the recommen ded daily nutrient allowance (RDNA). The results show that the intakes of c alcium and vitamin E of this group of people fall far below RDNA. Copyright (C) 2001 John Wiley & Sons, Ltd.