Instrument accuracy and calibration¶

The atlas describes how each value was recorded, but not yet how accurate the instrument behind it was. That needs the calibration and quality-control records of every device, which are not in the release.

Background¶

A recorded value differs from the true one for two reasons: how it was written down (resolution: rounding, heaping, sampling) and how well the instrument measured it (accuracy: bias, imprecision, drift between calibrations). The atlas so far covers the first. For accuracy it has, at best, manufacturers' specifications, and no variable yet carries an accuracy figure.

Data¶

None from the release. The VitalDB data hold the readings, not the instruments' calibration history.

Discussion¶

The hospital will have the records that would settle this: laboratory internal quality control and external quality assessment for each analyser, biomedical engineering's calibration and maintenance logs for monitors, pumps, ventilators and scales, and the dates and versions of each device in service. Summarised per device and period, they would give each variable an accuracy term (a bias and an SD, and how they changed over time) to sit beside its resolution model. Ideally they would be published in the same form as this atlas, so that each variable's uncertainty is complete.

Limitations¶

Until such records are available, every value's uncertainty in the atlas is a lower bound: resolution only.

Open questions¶

• Every instrument within its calibration (untestable assumption). The atlas treats each instrument as accurate: no bias, no drift between calibrations, imprecision ignored. The release cannot test this. Calibration and quality-control records for every measuring device used in the VitalDB cases (laboratory analysers, monitors, infusion pumps, ventilators, scales and stadiometers) would replace the assumption with a measured accuracy for each variable. This is beyond the scope of this work, but the hospital will hold the records, and publishing them in a metrology atlas like this one would make every variable's uncertainty complete.

Tags: value side