ABSTRACT
A clear distinction should be made between the terms “precision” and “accuracy” when they are applied to methods of analysis. Precision refers to the reproducibility of a method when it is repeated on a homogeneous sample under controlled conditions, regardless of whether or not the observed values are widely displaced from the true value as a result of systematic or constant errors present throughout the measurements. Precision can be expressed by the standard deviation. Accuracy refers to the agreement between the amount of a component measured by the test method and the amount actually present. Relative error expresses the difference between the measured and the actual amounts, as a percentage of the actual amount. A method may have very high precision but recover only a part of the element being determined, or an analysis, although precise, may be in error because of poorly standardized solutions, inaccurate dilution techniques, inaccurate balance weights, or improperly calibrated equipment. On the other hand, a method may be accurate but lack precision because of low instrument sensitivity, variable rate of biological 107activity, or other factors beyond the control of the analyst.
