Determine 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, defining the contribution to reproducibility, defining the contribution to comparability, and displaying the result.
Before you can perform a calculation, measurement data must be available for the selected test profile within the selected time period.
Opening the measurement uncertainty report¶
In the left-hand menu, under Evaluation, open the Measurement Uncertainty area.
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 is included in the evaluation. Optionally, you can select a device to narrow down the display in step 2.
Under Comparability method, select the basis on which the contribution to comparability should be calculated:
- Reference material – comparability is calculated based on measurement series on lab samples with stored certificate data.
- Interlaboratory comparison – comparability is calculated based on recorded interlaboratory comparison participations.
Select Next to continue.
Info
If no measurement data is available for the selected test profile within the selected time period, the next step cannot be performed. The same applies if no interlaboratory comparison participations exist and the interlaboratory comparison method has been selected. First record measurement data under Record measurement series or Record interlaboratory comparison participation, or adjust the time period.
Step 2: Reproducibility¶
ConCertainty displays all lab samples for which measurement data is available under the selected test profile within the selected time period – each with device and number of measurements.
Select Select next to the lab sample that should be used as the basis for the reproducibility contribution. The selection is limited to one sample. Selecting the sample simultaneously 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 lab sample with stored certificate data, used to calculate the contribution to comparability.
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 made individual assignments.
If a parameter should not be included in the calculation, activate the Exclude checkbox in the corresponding row.
Info
Only lab samples with stored certificate data are available as comparability samples. If no measurement data is available for a parameter on such a sample, the comparability contribution for this parameter is automatically omitted.
Method: Interlaboratory comparison¶
ConCertainty displays all interlaboratory comparison 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 interlaboratory comparison participations are recommended. ConCertainty will indicate if the selection is 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 results 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 used in the calculation. The displayed characteristics depend on the selected method:
Reference material method:
| Characteristic | 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 |
Interlaboratory comparison method:
| Characteristic | 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 interlaboratory comparison 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.
Export 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 the metadata of the evaluation.
Start a new calculation¶
Select New calculation to start another evaluation. The current calculation will be discarded.