Systematic Error - the mean that would result from an infinite number of measurements of the same measurand carried out under repeatability conditions, minus a true value of the measurand.Error - the result of a measurement minus a true value of the measurand.The VIM definitions of error, systematic error, and random error follow: Therefore, the error can be estimated using equation 14.1 and the conventional true value.Įrrors in analytical chemistry are classified as systematic (determinate) and random (indeterminate). We can, however, estimate the error with the introduction of the 'conventional true value' which is more appropriately called either the assigned value, the best estimate of a true value, the conventional value, or the reference value. However, we cannot use equation 14.1 to calculate the exact error because we can never determine the true value. In addition, we can define error as the difference between the measured result and the true value as shown in equation 14.1 above. Since we can estimate the error, we can also estimate the accuracy of a measurement.
We therefore have the ability to make quantitative estimates of the error of a given measurement. However, we have the ability to make quantitative measurements. We often speak of accuracy in qualitative terms such a "good," "expected," "poor," and so on. We can then define the error in relation to the true value and the measured value according to the following equation: For example, lets call a measurement we make X I and give the symbol µ for the true value. However, we must add the reality of error to our understanding.
Our inability to perform perfect measurements and thereby determine true values does not mean that we have to give up the concept of accuracy. Since there is no perfect measurement in analytical chemistry, we can never know the true value. In theory, a true value is that value that would be obtained by a perfect measurement. "closeness of the agreement between the result of a measurement and a true value." The VIM reminds us that accuracy is a "qualitative concept" and that a true value is indeterminate by nature. The International Vocabulary of Basic and General Terms in Metrology (VIM) defines accuracy of measurement as. In analytical chemistry, the term 'accuracy' is used in relation to a chemical measurement.
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