Accuracy (More...)
Precision The capacity of the system to discriminate between different values of input; the "fineness" with which different values for input can be inferred from measured values of output. The pooled deviation of observed from expected values of output, all divided by the amplification, yields the "index of precision". The square of the reciprocal of the index of precision is the measure of the amount of information that can be delivered by the system. Specifically, precision is computed in several steps. First, the deviation of each observed value of output from the corresponding predicted value is squared; predicted values are determined from the curve relating input and output for all the data. The squared deviations are summed and divided by N-2, the number of "degrees of freedom"; the square root of the quotient is determined and is a number analogous to the standard deviation. This "root mean square deviation" is then divided by the slope of the input-output curve, i.e., the amplification, to yield the "index of precision"; it is assumed that the input-output relationship is linear. Comparability The ability of a system to deliver data that can be compared in standard units of measurement and by standard statistical techniques with the data delivered by other systems. While not a critical component of accuracy, comparability of data generated by a system is critical to evaluating its accuracy and usefulness. Economy The ability of a system to deliver data of high information content at a low overall cost per item of data; economy does not, of course, contribute to "accuracy" but is an important determinant of the practical usefulness of a system or method. | ||||
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