Key Word Definitions
| Term | Definition | Article | Page |
|---|---|---|---|
| Acceptable performance | Performance that lies clearly above the minimum standard and below the optimal standard | Analytical Quality– What Should We be Aiming for? | S5 |
| Analytical control | Process monitoring | Analytical Quality– What Should We be Aiming for? | S5 |
| Analytical noise | Signal produced in the absence of analyte | Limit of Blank, Limit of Detection and Limit of Quantitation | S49 |
| Analytical run (with respect to QC) | An interval, that is a period of time or series of measurements, within which the accuracy and precision of the measuring system is expected to be stable | The Quality Control System | S67 |
| Analytical sensitivity | Slope of the calibration curve | Limit of Blank, Limit of Detection and Limit of Quantitation | S49 |
| Assay boundary conditions | The combined characteristics (application, methodology and performance) of a method | Selection of a Suitable Assay | S17 |
| Bias | Difference between the mean replicate value and the assigned reference value | Basics of Estimating Measurement Uncertainty | S53 |
| Capability Index (Cps) | Allowable limit of error divided by the standard deviation of between-batch QC measurement | Use of Capability Index to Improve Laboratory Performance | S27 |
| Coefficient of variation (CV) | Standard measurement uncertainty (SD) divided by the absolute value of the measurand quantity value CV=SD/x or SD/mean value | Basics of Estimating Measurement Uncertainty | S53 |
| Combined standard measurement uncertainty (uc) | Standard measurement uncertainty that is obtained using the individual standard measurement uncertainties associated with the input quantities in a measurement model | Basics of Estimating Measurement Uncertainty | S53 |
| Coverage factor (k) | Number larger than one by which a combined standard measurement uncertainty is multiplied to obtain an expanded measurement uncertainty | Basics of Estimating Measurement Uncertainty | S53 |
| Coverage interval | Interval containing the set of true values of a measurand with a stated probability, based on the information available | Basics of Estimating Measurement Uncertainty | S53 |
| Degrees of freedom (df) | The number of replicates minus one | Imprecision Profiling | S33 |
| Delta check | Difference between consecutive results on the same patient | The Quality Control System | S67 |
| Diagnostic accuracy studies | Address how well a test identifies the target condition of interest i.e. agreement between a proposed (index) test and a reference standard for the ability to identify a target condition | Sensitivity, Specificity, Receiver- Operating Characteristic Curves, and Likelihood ratios: Communicating the Performance of Diagnostic Tests | S83 |
| Difference plot | Differences between the comparison estimates plotted against the mean of their values | Assessment of Bias with Emphasis on Method Comparison | S37 |
| Dynamic range | Analytical measurement range | Limit of Blank, Limit of Detection and Limit of Quantitation | S49 |
| Endogenous interference | Originates from substance found naturally in the patient’s sample | Interference Testing | S43 |
| Exogenous interference | Substances not naturally found in the patient’s specimen or arising from processes affecting the sample | Interference Testing | S43 |
| Expanded measurement uncertainty(U) | Product of a combined standard measurement uncertainty and a coverage factor larger than the number one | Basics of Estimating Measurement Uncertainty | S53 |
| Expert system | Computer programs that “represent and reason with knowledge of some specialist subject with a view to solving problems or giving advice”. Reference 7 cited in article | Expert Systems for Clinical Pathology Reporting | S105 |
| Hook effect | Antigen excess resulting in false low values | Interference Testing | S43 |
| Imprecision | Dispersion of results obtained from repeated measurements | Basics of Estimating Measurement Uncertainty | S53 |
| Imprecision profile | Expression of the precision characteristics of an assay over a range of concentration values | Imprecision Profiling | S33 |
| Inaccuracy | Relates to how closely a single measurement agrees with the true value | Assessment of Bias with Emphasis on Method Comparison | S37 |
| Interference | Substance or process that falsely alters an assay result | Interference Testing | S43 |
| Limit of Blank (LoB) | Highest apparent analyte concentration to be found when replicates of a blank sample containing no analyte are tested | Limit of Blank, Limit of Detection and Limit of Quantitation | S49 |
| Limit of Detection (LoD) | Lowest analyte concentration likely to be reliably distinguished from the LoB and at which detection is feasible | Limit of Blank, Limit of Detection and Limit of Quantitation | S49 |
| Limit of Quantitation (LoQ) | Lowest concentration at which the analyte cannot only be reliably detected but at which some predefined goals for bias and imprecision are met | Limit of Blank, Limit of Detection and Limit of Quantitation | S49 |
| Measurand | Quantity intended to be measured | Basics of Estimating Measurement Uncertainty | S53 |
| Measurement traceability | The property of the result of measurement or the value of a standard whereby it can be related to stated references, usually national or international standards, through an unbroken chain of comparisons all having stated uncertainties | Traceability of Measurement Results | S61 |
| Measurement uncertainty | Non-negative parameter characterising the dispersion of the quantity values being attributed to a measurand, based on the information used | Basics of Estimating Measurement Uncertainty | S53 |
| Metrology | Science of measurement | Basics of Estimating Measurement Uncertainty | S53 |
| Negative likelihood ratio (LR-) | Ratio of the proportion of patients who have the target condition and test negative to the proportion of patients without the target condition who also test negative = (1- sensitivity)/specificity | Sensitivity, Specificity, Receiver- Operating Characteristic Curves, and Likelihood ratios: Communicating the Performance of Diagnostic Tests | S83 |
| Negative predictive value (NPV) | Proportion of negative results that are true negatives i.e. do not have the target condition = TN/(TN + FN) | Sensitivity, Specificity, Receiver- Operating Characteristic Curves, and Likelihood ratios: Communicating the Performance of Diagnostic Tests | S83 |
| Partitioning of a reference interval | Use of separate intervals for different sub- populations | Reference Intervals | S93 |
| Positive likelihood ratio (LR+) | Ratio of the proportion of patients who have the target condition and test positive to the proportion of patients without the target condition who also test positive = sensitivity/ (1-specificity) | Sensitivity, Specificity, Receiver- Operating Characteristic Curves, and Likelihood ratios: Communicating the Performance of Diagnostic Tests | S83 |
| Positive predictive value (PPV) | Proportion of positive results that are true positives i.e. have the target condition = TP/(TP + FP) | Sensitivity, Specificity, Receiver- Operating Characteristic Curves, and Likelihood ratios: Communicating the Performance of Diagnostic Tests | S83 |
| Post-analytical control | Product monitoring | Analytical Quality– What Should We be Aiming for? | S5 |
| Pre-analytical control | Input monitoring | Analytical Quality– What Should We be Aiming for? | S5 |
| Precision | Concept of variation around a central value. Measured as imprecision | Evaluating Assay Precision | S23 |
| Prevalence | Prior probability | Sensitivity, Specificity, Receiver- Operating Characteristic Curves, and Likelihood ratios: Communicating the Performance of Diagnostic Tests | S83 |
| Quantity | Property of a phenomenon, body or substance, where the property has a magnitude that can be expressed as a number and a reference | Basics of Estimating Measurement Uncertainty | S53 |
| Receiver- operating characteristic (ROC) curve | Compare sensitivity versus specificity across a range of values for the ability to predict a dichotomous outcome
Graphical display of true positives versus false positives across a range of cut-offs and of selecting the optimal cut-off for clinical use |
Sensitivity, Specificity, Receiver- Operating Characteristic Curves, and Likelihood ratios: Communicating the Performance of Diagnostic Tests | S83 |
| Repeatability | Closeness of agreement between results of successive measurements obtained under identical conditions | Evaluating Assay Precision | S23 |
| Reporting interval (RI) | Incremental value chosen for reporting analyte concentration | Significant Figures | S89 |
| Reproducibility | Closeness of agreement between results of successive measurements obtained under changed conditions (time, operator, calibrator, reagent and laboratory) | Evaluating Assay Precision | S23 |
| Sensitivity | “Positivity in disease”. Proportion of subjects with the target condition who have positive test results = TP/(TP + FN) | Sensitivity, Specificity, Receiver- Operating Characteristic Curves, and Likelihood ratios: Communicating the Performance of Diagnostic Tests | S83 |
| Six-Sigma concept | Six SD on each side of the mean of the process should fit within the designated limits | Use of Capability Index to Improve Laboratory Performance | S27 |
| Specificity | “Negativity in health”. Proportion of subjects without the target condition with negative test results = TN/(TN + FP) | Sensitivity, Specificity, Receiver- Operating Characteristic Curves, and Likelihood ratios: Communicating the Performance of Diagnostic Tests | S83 |
| Standard measurement uncertainty (u) | Measurement uncertainty expressed as a standard deviation | Basics of Estimating Measurement Uncertainty | S53 |
| Total error | Between-assay error | Imprecision Profiling | S33 |
| True value | Quantity value consistent with the definition of quantity | Basics of Estimating Measurement Uncertainty | S53 |
| Trueness | Closeness of agreement between the average of an infinite number of replicate measured quantity values and a reference quantity value | Basics of Estimating Measurement Uncertainty | S53 |
| Undesirable performance | Performance that lies only slightly above the minimum standard | Analytical Quality- What Should We be Aiming for? | S5 |
| Within- laboratory precision | Total precision within the same facility using the same equipment | Evaluating Assay Precision | S23 |