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close this book Food Composition Data: A User's Perspective (1987)
close this folder Other considerations
close this folder Consideration of food composition variability: What is the variance of the estimate of one-day intakes? Implications for setting priorities
View the document (introductory text)
View the document Introduction
View the document Magnitude of the reported variability of composition
View the document Impact of composition variation on a one-day food intake
View the document Additional impact of a random error in intake estimation
View the document Some implications for data analyses
View the document Validation of food intake data: implications of food composition variation
View the document Systematic errors in food composition data
View the document Relevance to priorities for food composition data
View the document Conclusions
View the document References

Magnitude of the reported variability of composition

Magnitude of the reported variability of composition

Table 1 presents some estimates of the standard deviation of food composition generated from the standard errors and number of assays presented in the new USDA data bases [9]. This tabulation is impressionistic rather than systematic - that is, an examination of some sample foods rather than a thorough examination of all foods was carried out in order to generate the estimates. Empirically it was observed that for each of the nutrients there was a distinction between the CV at low concentrations and at higher concentrations. This was probably due to the impact of methodologic error when concentration was low. In table 1, estimates are presented above and below arbitrary cut-off points to illustrate this phenomenon.

It can be seen that the very high CVs are associated with the low concentrations of nutrients. Above the arbitrary cut-off points the nutrients fall into two classes as far as CVs are concerned. These probably represent the general magnitude of the biological variability of food composition.