Determining measurement uncertainty¶
To determine the measurement uncertainty for a test profile, ConCertainty guides you through a four-step process: selecting the data basis and method, determining the reproducibility contribution, determining the comparability contribution, and displaying the result.
Before you can perform a calculation, measurement data for the selected test profile must be available for the selected period.
Opening the measurement uncertainty report¶
In the left-hand menu, under Evaluation, open the Measurement Uncertainty section.
Step 1: Selection¶
Select the test profile for which you want to determine the measurement uncertainty. The evaluation period is pre-filled with the last three months and can be adjusted using Date from and Date to – it determines which measurement data are included in the evaluation. Optionally, you can restrict the laboratory samples shown in step 2 by selecting a device.
Under Comparability method, select the basis on which the comparability contribution should be calculated:
- Reference material – comparability is calculated based on measurement series on laboratory samples with stored certificate data.
- Proficiency test – comparability is calculated based on recorded proficiency test participations.
Select Next to continue.
Info
If no measurement data are available for the selected test profile in the selected period, the next step cannot be performed. The same applies if no proficiency test participations are available and the proficiency test method has been selected. First record measurement data under Recording a measurement series or Recording a proficiency test participation, or adjust the period.
Step 2: Reproducibility¶
ConCertainty displays all laboratory samples for which measurement data are available under the selected test profile in the selected period – each with device and number of measurements.
Select Select next to the laboratory sample to be used as the basis for the reproducibility contribution. The selection is limited to one sample. Selecting the sample also determines the device for the entire evaluation.
Info
For a robust result, a sample with as many measurements as possible should be selected.
Step 3: Comparability¶
The content of this step depends on the method selected in step 1.
Method: Reference material¶
ConCertainty displays a parameter table with the mean value and standard deviation of the measured values from step 2. For each parameter, you can assign a comparability sample – i.e. a laboratory sample with stored certificate data, which is used to calculate the comparability contribution.
Using the All parameters selection field, you can assign the same comparability sample to all parameters at once.
Warning
The global assignment via All parameters overwrites all previously individually made assignments.
If a parameter should not be included in the calculation, activate the Exclude checkbox in the corresponding row.
Info
Only laboratory samples with stored certificate data are available as a comparability sample. If no measurement data are available for a parameter on such a sample, the comparability share for this parameter is automatically omitted.
The selection of a comparability sample per parameter is limited to laboratory samples whose certificate value for the respective parameter has the same unit as the parameter and lies within ±25% of the mean value of the reproducibility measurement series. If no suitable reference material is available for a parameter that meets both conditions, the selection field remains empty. In this case, you can exclude the parameter from the calculation using Exclude.
Info
The All parameters selection field offers all laboratory samples with certificate data, regardless of unit or concentration range. However, after the assignment, the restriction still applies per parameter: for parameters where the selected sample does not match in unit and concentration, the row remains unassigned. In this case, check the affected rows and assign a suitable reference material or exclude the parameter.
Method: Proficiency test¶
ConCertainty displays all proficiency test participations recorded for the selected test profile. For each participation, it is visible how many parameters are fully available.
Select one or more participations using the respective checkbox.
Info
For a statistically reliable calculation, at least 6 proficiency test participations are recommended. ConCertainty indicates when the selection falls below this minimum number. The calculation can still be performed – however, the significance of the results is limited in this case.
Select Start calculation to calculate the result.
Step 4: Result¶
The result table shows the following for each parameter:
| Column | Meaning |
|---|---|
| Reproducibility u_R,w | Contribution of reproducibility to the measurement uncertainty |
| Comparability u_b,rel | Contribution of comparability to the measurement uncertainty |
| Combined uncertainty u_c,rel | Measurement uncertainty composed of both contributions |
| Expanded uncertainty U_rel | Expanded measurement uncertainty (combined uncertainty × k-factor) |
Using Details next to each parameter, you can view the input values of the calculation. The displayed characteristics depend on the selected method:
Reference material method:
| Parameter | Meaning |
|---|---|
| Mean value | Mean value of the measurement series (reproducibility) |
| Standard deviation | Standard deviation of the measurement series |
| Number of measurements | Number of measurements included |
| Reference value | Certified reference value of the comparability sample |
| Bias | Absolute deviation of the mean value from the reference value |
| Relative bias | Bias as a percentage of the reference value |
Proficiency test method:
| Parameter | Meaning |
|---|---|
| Mean value | Mean value of the measurement series (reproducibility) |
| Standard deviation | Standard deviation of the measurement series |
| Number of measurements | Number of measurements included |
| Number of participations | Number of selected proficiency test participations for this parameter |
| D_rms,rel | Root mean square of the relative deviations of the own values from the consensus value across all selected participations |
| u_Cref,rel | Relative contribution of the uncertainty of the consensus value |
| u_b,rel | Relative contribution of comparability to the measurement uncertainty |
Using the Relative and Absolute buttons, you can switch between relative and absolute display of the results.
Exporting the result as PDF¶
Select Generate PDF to export the measurement uncertainty report. Your browser's print dialog opens. There, select Save as PDF (or a comparable option) as the printer to save the report as a PDF file.
The report contains an overview of all parameters with the calculation results, as well as the input values used and metadata of the evaluation.
Starting a new calculation¶
Select New calculation to start another evaluation. The current calculation will be discarded.