Within-person variation in daily dietary intake of boys from Finland, the Netherlands, Italy, the Philippines and Ghana.

We have studied the within-person variation in daily dietary intake of energy, protein, fat, carbohydrate, cholesterol, saturated and polyunsaturated fatty acids in 8- and 9-year-old boys from five countries, using record and recall methods of dietary assessment. The average within-person coefficients of variation ranged from 19 to 31 per cent of the mean intake of energy, protein and carbohydrate; from 43 to 77 per cent of the mean intake of cholesterol, from 28 to 50 per cent of the mean intake of saturated fatty acids, and from 37 to 105 per cent of the mean intake of polyunsaturated fatty acids. Some of this variation may have been due to differences in the methods used to assess dietary intake. The day of the week on which food intake is estimated can also influence the number of measurements required to estimate precisely an individual's intake of energy or specific nutrients. From the results of this study it can be shown that it is not always justified to assume that every person in a population has the same within-person variance. This may lead to an underestimation of the number of measurements needed to estimate individual intakes. The results of this study are useful in the planning of dietary surveys when decisions are to be made about methods of data collection, sample size and length of the study, and also in the analysis and interpretation of the results of dietary surveys.