About Precision
Other Names - Repeatability Test, Reproducibility Test, Consistency Test, Variability Test, Precision Study, Repeatability Study, Reproducibility Study, Intra-assay Precision, Inter-assay Precision, Consistency Measurement.
Precision refers to the consistency of test results when the same test is repeated under identical conditions. It measures the reproducibility of categorical outcomes, ensuring the method produces the same results consistently across different runs and operators. Verified precision is essential for the reliability of diagnostic tests.
The precision experiment in Method Verification (MV) assesses the consistency and repeatability of a test method. It involves repeatedly testing the same sample under identical conditions to determine the variability in the results. Precision experiments can be conducted within a single run (Within Day Precision) or across multiple runs (Between Day Precision), providing insights into the method's reliability over time and different conditions. The goal is to ensure that the test produces stable and consistent results, minimizing random errors.
High precision is crucial for the reliability of any diagnostic test, as it ensures that repeated measurements yield similar results, thereby enhancing confidence in the test method. This experiment typically involves calculating the standard deviation or coefficient of variation (CV) of the repeated measurements. By demonstrating low variability, the precision experiment confirms that the test method is robust and dependable for clinical or diagnostic use.
The experimental design for Precision involves repeatedly testing multiple samples under consistent conditions to assess the consistency of categorical outcomes, such as positive or negative results, over time and across different operations.
Acceptance Criterias
Samples
In Cualia’s Precision Experiment the experimental design should be considered first with the number of Samples. Each sample should be of a different concentration to assess the precision at different levels.
It is recommended to use at least 3 samples: a blank, a low concentration and a high concentration. 2 samples may be used if the assessor confirms acceptability.
Days and Results/Replicates per Day
The number of days and measurements per day that will be performed for each sample/level. It is best to use a number of days and results per day that will effectively evaluate the precision of your instrumentation.
Min. Between Day Agreement (%)
The Min. Between Day Agreement % is the Agreement % threshold for each sample across all of its days and replicates for the sample to be considered passed.
The Standard 5x5 Precision Experiment
Oftentimes, the Standard 5x5 approach is the way to go. This follows a 3x5x5 format of 75 replicates. It is a standard design used in method validation to assess the precision of a measurement method. This design involves three distinct samples at different concentrations, each performed on five different days, with five replicates tested in each run.
The Standard 5x5 is the default setting in Cualia MVs.
2. Sample Selection
In general practice is it often acceptable to use controls as samples. However this should be discussed with the assessor to confirm.
3. Testing Samples
Measure each sample on a reference method (reference) and on your new instrumentation (actual) the appropriate number of times.
For example if running a 3x4x5 experiment 3 samples will be run on the MV test 5 times on 4 separate days. It is recommended to make variations in time of day and operator to ensure robustness and rule out operator biases.
4. Use the Cualia MV App
Make sure the data is entered into the experiment with the right acceptance criterias.
Structure
- Samples Tabs - Navigate between samples/levels from the Samples Tabs. These will show different tables for each of the samples.
- Sample Label - The Sample Label field allows for given the sample/level an identifier.
- Reference Value - Expected value from the reference. In qualitative tests this value should be the same as the actual measurements.
- Data Table - Area where measurement values may be entered. See the Data Table section below for more information.
- Sample Results - Shows the label, reference value, the number of results and the agreement % for the sample/level. The numbers will turn green when the acceptance criterias are satisfied.
- Experiment Results - Overall results of the experiment including the number of samples with measurements, results and the agreement % across all results.