Quality Definitions

Accuracy – Agreement between the best estimate of a quantity and its true value. (Westgard)

Allowable total error – An analytical quality requirement that sets a limit for both the imprecision and inaccuracy that are tolerable in a single measurement or single test result. (Westgard)

Analytical error – The difference between the estimated value of a quantity and its true value. (Westgard)

Assayed control material – A control solution or control material for which the manufacturer defines the results expected for different tests and different methods. (Westgard)

Bias – A systematic difference between an observed value and some measure of the truth. (Westgard)

Coefficient of variation, %CV – The relative standard deviation, ie, the standard deviation expressed as a percentage of the mean. CV=100(S/X). (Westgard)

Control chart – A graphical method for evaluating whether a process is or is not in a state of statistical control. The determinations are made through comparison of the values with control limits. (Westgard)

Control limits – Lines on a control chart used to assess the control status of a method; commonly calculated as the mean of the control material plus or minus a certain multiple of the standard deviation observed for that control material. (Tietz 6th ed.)

Control procedure – The protocol and materials necessary for an analyst to assess whether a method is working properly and patient results can be reported. (Tietz 6th ed.)

Control rules – a decision criterion used to interpret quality control data and make a judgement on the control status of an analytical run. (Tietz 6th ed.)

Error – a deviation from truth, accuracy, or correctness; a mistake.

Error detection – A performance characteristic of a QC procedure that describes how often an analytical run is rejected when results contain errors in addition to the inherent imprecision of the method. (Tietz 6th ed.)

Error of measurement – Result of a measurement minus a true value of a measure.

Gaussian Curve, Gaussian distribution, Normal curve, normal distribution – Refers to the symmetrical bell-shaped distribution whose shape is given by a specific equation in which the mean and standard deviation are variables. (Westgard)

Levey-Jennings control chart – A commonly used control chart in which individual control measurements are plotted directly on a control chart with limit lines drawn either as mean +/-2s or mean+/-3s.(Westgard)

Mean – the arithmetic average of a set of values. (Westgard)

Median – The middle result in a list of ascending or descending numbers.

Mode – The most frequent result in a list of values.

Path of Workflow – Sequential processes in a healthcare organization or service’s activities that transfer a physician’s order into the service’s product.

Policy – A documented statement of overall intentions and directions defined by those in the organization and endorsed by management.

Post service processes – Processes following service realization including results review, formatting reports or labels, authorization of results, reports, or drugs for release, reporting of results, transmission of the results, and storage of samples.

Precision – The agreement between replicate measurements. It has no numerical value. (Westgard)

Preservice processes – Processes preceding service processes, from the clinician’s request, including the ordering requisition, preparation of the patient, collection of any samples, transportation of samples or patients to and within the clinical service area, and ending when service realization starts. (eg, lab testing).

Procedure – Specified way to carry out an activity of a process.

Process – Set of interrelated or interacting activities that transform inputs into outputs.

Quality Control – Part of quality management focused on fulfilling quality requirements. (CLSI)

Quality Control – Running samples with known values and expected outcomes to make sure a process is getting the intended results. The results are compared to expected results to see if they fall within an acceptable range.

(Bio-Rad)Random error – An error that can be either positive or negative, the direction and exact magnitude of which cannot be exactly predicted. (Westgard)

Service processes – Activities related to providing the service’s product.

Shift -consecutive observations on a QC chart above or below the mean. There should be at least 8 values before it is called a shift.

Standard deviation – A statistic that describes the dispersion or spread of a set of measurements about the mean value of a Gaussian or normal distribution. (Westgard)

Statistical quality control – The aspects of quality control in which statistics are applied, in contrast to the broader scope of quality control which included many other procedures, such as preventive maintenance, etc. (Westgard)

Statistical tools – Methods and techniques used to generate, analyze, interpret, and present data.

Systemic Error – An error that is always in one direction and is predictable ( in contrast to random errors). (Westgard)

Total error – The net or combined effect of random and systematic errors. (Westgard).

True value – Generally used to indicate that this is the correct analytical concentration or result. (Westgard)

Trend – consecutive points on a control chart that show a non-random pattern and are moving in one direction.

Within-run imprecision – The random error observable within the time period of a single analytical run. (Westgard)