11 Apr Refers To The Agreement Of A Particular Value With The True Value
A set of measurements is accurate when all measurements are very similar, i.e. when there is a small range of values. Repeatability and reproducibility are included in the definition of accuracy and are used to describe the variability of the measurement method. In general, reproducibility implies more effects on variability than repeatability. It is defined as the resulting variation of a measurement process when performed in different instruments, operators, environments and periods (measurement conditions). On the other hand, repeatability refers to the variation that occurs even when effort is needed to keep the device, operator and environment constant and shorten the measurement period. For example, the iron cube has a real value of 7.90 ± 0.01 g the actual value is between 7.90 – 0.01 – 7.89 g and 7.90 – 0.01 – 7.90 g. A precise value for the mass of iron would be between 7.89 g and 7.91 g. An inaccurate value for the mass of iron would be less than 7.89 g or greater than 7.91 g. If we know the tolerance of a real measure, we can decide that the determined value is accurate if it falls within the tolerance levels of the real measure, and imprecise if it is outside the tolerance levels of the actual value. ISO 5725, entitled “Truth and Accuracy) of Measurement Methods and Results, uses the combination of two terms, “truth” and “precision” (Figure 1), to describe the accuracy of a measurement method.
According to ISO 5725, “truth” refers to the consistency between the arithmetic average of a large number of test results and the actual or accepted baseline . “Precision” refers to the agreement between the different test results. For example, the actual value of the mass of an iron cube is, as we know, 7.90 g. They weigh the same cube of iron and determine that it has a mass of 7.90 g. The actual value and value are the same, so we can say that we have accurately determined the mass of the iron cube. To determine accuracy, we must compare each student`s score with the actual value indicated as 25.23oC. Since we have a series of different measurements with the same thermometer by the student in the same laboratory, we could start with the student`s average results: a measuring device is both accurate and accurate (or simply accurate according to the general definition of that term) when it produces measurements that are all grouped closely around the reference value (“true”) with a defined error range.