Reevaluation of the Variable Component of the Systematic Error Calls for Paradigm Change in Clinical Laboratory Quality Control

The existence of the variable component of the systematic error (VCSE) is known since 1963, but seems to be a kind of taboo: neither has definition in VIM, nor is present in equations, being considered transformed in time into random error. Present study using methods of mathematical statistics, computer simulations and examples from the day-to-day practice of the author makes an attempt to reevaluate its role and significance in the QC in clinical laboratory. “The bias” (which one?) it is a definitional uncertainty, because it is time-variable. Making clear distinction between bias measured in repeatability respective reproducibility within laboratory (RW) conditions as in case of standard deviations, and also separating constant and variable subcomponents of the systematic error, two sets of error parameters are obtained each set being consistent with the measurement conditions. The link between them is the time-variable VCSE function. The conditions of calculations and predictions based on them must be consistent with the conditions of their determination, to avoid the redundant use. Being consequent, several differences can be discovered between the constant and the variable component of the systematic error respective random phenomena, also between variable and random error components. The variable components of the systematic errors are cyclical, mostly predictable variations (shifts and drifts) in the daily mean. However, it is presented a direct method to determine the SD of the VCSE, its easiest calculation is possible from accurate values of s r and s RW . There are presented methods to calculate s r and s RW from long term data. As conclusion there is necessary a new paradigm of the QC in clinical laboratory based on the proposed error model. Motto “Everything Should Be Made as Simple as Possible, But Not Simpler” (A. Einstein) .