Linearity Information and Courses from MediaLab, Inc.
These are the MediaLab courses that cover Linearity and links to relevant pages within the course.
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| Calibration Curve Standards are also used to determine the linearity of the testing instrument. This is done by plotting a calibration or standard curve. Most testing instruments must be operated within a linear range. The Clinical and Laboratory Standards Institute or NCCLS defines linearity as “the measure of the degree to which a curve approximates a straight line.The examples to the right show linearity because a change along the x-axis shows a corresponding change along the y-axis, whether the x-value is low or high.
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| Linearity Example Looking at the example to the right, we can see that the instrument on which we are doing a calibration curve is linear up to 1000 mg/100ml of blood for a particular analyte. Accordingly, we can be fairly certain that any results obtain up to 1000 milligrams are accurate. Above 1000 milligrams our curve begins to bend. This means that any results greater than 1000mg may not reflect a true measurement of the analyte being tested. The specimen must be diluted down to the linear range. | View Page |
| Non-linear Calibration Curves Linear calibration curves are more desirable because they result in the best accuracy and precision. Some testing methods, however, do have nonlinear calibration curves. When that is the case, more calibration standards are needed to achieve desirable precision. Regardless, linearity is not to be used as a tool for calibration verification, accuracy assessment, or establishing a reportable range.
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| Verification for Non-waived Testing Laboratories that do non-waived testing must verify that they can obtain performance specifications comparable to those established by the manufacturer. Generally this can be accomplished by doing split sample comparison studies with another laboratory to estimate any inaccuracy or bias, plus linearity studies to estimate imprecision and determine the reportable range. The laboratory can do studies to determine its own reference ranges or the laboratory director can document that the manufacturer’s ranges are appropriate.For those laboratories doing non-waived tests that have been modified or developed in-house, additional verification studies are required.
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| Linearity David S. Plaut further refines the definition. He states that linearity is “a line that does not change slope between the high point and next lowest one and passes through zero.” The formulation of a calibration curve will vary according to the procedure, but it should be based on at least three known values—more if necessary. | View Page |
| The extent to which a measurement agrees with the true value of the analyte being measures is known as: | View Page |
| Which of the following meets the strict definition of linearity given by Plaut? | View Page |