Sources of variation in iron absorption measurements and methods of controlling them have been reviewed. There are marked differences in the mean level of absorption in different individuals and appreciable day-to-day variation in absorption in the same individual. Intersubject variations can be reduced by the selection of individuals with a more uniform iron requirement, but large variations remain which can be dealt with only by applying appropriate statistical methods to the skewed data obtained and by studying sufficient subjects to provide statistical validity to the results. Comparative studies of the availability of food iron are best carried out against a reference standard in the same subject, and intrasubject variations can be reduced by multiple dose administration.

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