Determination of intra-/inter-individual variability and its effect on the number of days required to assess the usual intake of a school children population
1997
Bellu, R. | Cucco, I.
The inaccuracy with which individuals' usual intake of nutrients influences the assessment of the relation between nutrients as independent variables and outcome as dependent variables. Intra- and inter-individual variability are used to assess such inaccuracy but data for the pediatric population are scant. Intra- and inter-individual variability was therefore investigated in a pediatric population attending the primary school. A seven-day weighted food record was completed twice by the mothers of 110 children over a six-month period. The total variance of each nutrient was subdivided into intra- and inter-individual components by analysis of variance for repeated measure and the coefficients of variability within (CVintra) and between (CVinter) individuals were calculated along with the number of days required to describe the individual's usual intake. The nutrients were considered both as raw intake and nutrient density (nutrient expressed in proportion to energy). Many nutrients displayed an intra-/inter-individual variability ratio > 1, not amenable to be altered by adjustment for total caloric intake. A calorie 10% error margin or less should be expected by using a 20-day time frame. On the other hand most nutrients present a 10% error over thirty-day studies. For many nutrients, bracketing the error within the 10% margin would require an unrealistic time frame. The adjustment for calorie intake reduced the number of days required for the dietary record. In conclusion, in school children, within a 7-day study design the intake of most nutrients could be calculated with an error margin as wide as 30% and for some nutrients the margin is even wider.
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