Inter- and intra-individual variability in food intake of elderly people in Perugia (Italy).

It has been shown that each individual has a considerable day-to-day variation (intra-individual variation) in his or her level of food consumption. A large intra-individual variation has adverse effects on the reliability of research studies. The effect of the intra-individual variation can be minimized by taking food intake records over several days. An increase in the number of days entails higher costs, and this could limit the practicability of the study. In the recent literature on the methodology of dietary surveys, there is a growing interest in the estimation of the number of days required to conduct a reliable dietary survey. Recent developments in statistical theory allow the problem of large intra-individual variability to be overcome. These new statistical techniques require knowledge of the intra- and inter-individual variability and the appropriate adjustment of the statistical results. The aim of the present study was to evaluate the number of days of recorded intake required to obtain an estimate of the components of variance (the inter-individual and the intra-individual variability) focusing on foods rather than nutrients.