Errors of Anthropometric Measurements

All anthropometric measurements should be made as accurately as possible. Measurement errors may result in the misclassification of subjects' nutritional status or may lead to changes in nutritional status over time being over- or underestimated. Very precise and accurate measurements are needed for nutrition research and in some clinical situations. The same degree of precision may not be possible in nutritional screening and surveillance programs in field studies. Errors in making measurements arise from the equipment, the physical state and age of the subjects, the time of day when the measurements are made, misreading of measurements by the observer, and as a result of rounding up or down to the nearest half or whole integer. These technical errors of measurement (TEM) vary with the age of the subjects, the measurements being made, and between (inter-) and within (intra-) observers. Values for a particular anthropo-metric measurement of a group of people by age and sex can be considered accurate if the inter- and intraobserver error is close to a reference value for TEM in a series of repeated measurements and if there are no biases in the measurement. For measurements of subjects outside the age range, the coefficient of variability (R) can be calculated as R = 1 - [(TEM)2/(SD)2], where SD is the total inter-subject variance including measurement error. It has been recommended that an R of 0.90, that is a measurement 90% error-free, is an acceptable lower limit of accuracy, although an intraobserver R of 0.95 might be more realistic in some circumstances.

TEM can be minimized by careful training of all observers and by making measurements using appropriate equipment in triplicate and then calculating the mean. If measurements for a research study are to be made by more than one person, the interobserver measurements made must be comparable. R can be calculated for interobserver variability by making a series of measurements.

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