Factors Contributing To the Acceptable Range Of Results
There are several factors that can contribute to test result obtained from a particular instrument. These factors may be associated with the instrument design, the calibrator/control formulation, the operating environment in the laboratory, and the operator. Among the more significant factors are those listed below:
Error Contribution of the Calibrator/Control
There is a tolerance associated with formulating a calibrator/control due to normal variations in the production and quality control processes. This tolerance can affect the mean value obtained from testing multiple samples of the calibrator/control, and is independent of any specifications associated with the instrument.
Error Contribution of the Osmometer
The linearity and repeatability specifications for the osmometer also affect the test results. These specifications are independent of the formulation tolerance of the calibrator/control.
The linearity (accuracy) specification defines the maximum deviation of the mean of an actual set of test data from the nominal value of the calibrator/control being tested. It is frequently expressed as a percentage of the nominal value of the calibrator/control.
The repeatability (precision) specification defines the limits of variation for any individual test result with respect to the calculated mean of a series of results. Repeatability is frequently expressed as a standard deviation (S.D. or s), with 1 standard deviation (1 S.D. or 1s) incorporating approximately 67% of a normally distributed population relative to the calculated mean of the results. For any given series of tests it is possible to have individual test results that lie beyond this 1 standard deviation limit. When establishing allowable limits for test results that encompass population percentages higher than 67%, multiples of the repeatability specification should be used in the calculation (i.e. for results that encompass 95% of the population, a repeatability value equivalent to 2 standard deviations should be used).