An investigation of the methods for estimating usual dietary intake distributions : a thesis presented in partial fulfillment of the requirements for the degree of Master of Applied Statistics at Massey University, Albany, New Zealand
The estimation of the distribution of usual intake of nutrients is important for developing nutrition
policies as well as for etiological research and educational purposes. In most nutrition surveys only a
small number of repeated intake observations per individual are collected. Of main interest is the longterm
usual intake which is defined as long-term daily average intake of a dietary component. However,
dietary intake on a single day is a poor estimate of the individual’s long-term usual intake.
Furthermore, the distribution of individual intake means is also a poor estimator of the distribution of
usual intake since usually there is large within-individual compared to between-individual variability in
the dietary intake data. Hence, the variance of the mean intakes is larger than the variance of the
usual intake distribution. Essentially, the estimation of the distribution of long-term intake is equivalent
to the estimation of a distribution of a random variable observed with measurement error.
Some of the methods for estimating the distributions of usual dietary intake are reviewed in detail and
applied to nutrient intake data in order to evaluate their properties. The results indicate that there are a
number of robust methods which could be used to derive the distribution of long-term dietary intake.
The methods share a common framework but differ in terms of complexity and assumptions about the
properties of the dietary consumption data. Hence, the choice of the most appropriate method
depends on the specific characteristics of the data, research purposes as well as availability of
analytical tools and statistical expertise.