1. Parameters of Measurement Accuracy

To address quality assurance issues, there are two sets of numbers of interest.

The first set is the degree of refinement of a measure. That is, the degree to which a measure is recorded. For example, infant weight is recorded to 0.01 kg, 10 grams, or 1/2 ounce. If a newborn infant was weighed only to 0.1 kg, 100 grams, or 3 ounces, a rate of weight gain of less than 100 grams would not be reflected in the measure.

The tolerance of a measure is the difference between two measures that is accepted as reasonable accuracy. The tolerance of a measure is generally larger than the degree of refinement of a measure. For example, the weight of an infant is recorded as 3.12 kg and on re-measuring it is recorded as 3.13 kg. These measures are within an acceptable tolerance. If, however, the infant was weighed at 3.12 kg and a second measure was 3.2 kg, the infant should be re-weighed. If the third measure was recorded as 3.11 kg, the average of the two closest measures would be recorded.

The tolerance of a measure is generally larger for measures of older children and adolescents because small changes are less critical for the interpretation of growth.