What defines a systematic error in the measurement process during XRF reading?

A systematic error in the measurement process, particularly during XRF (X-ray fluorescence) readings, is defined by consistent inaccuracies that arise from the inherent properties of the materials being analyzed. The substrate effect refers to how the material underlying the lead-based paint can influence the measurement results. This effect can cause the XRF device to misinterpret the composition of the paint, leading to a bias in the readings.

When the substrate characteristics (such as its chemical composition, density, and thickness) differ significantly from those expected by the XRF device for accurate measurement, this can consistently skew the results in a particular direction. Therefore, it is critical to understand the nature of the substrate when interpreting XRF readings.

This understanding highlights how systematic errors are not random or due to analyst bias, but rather result from predictable and consistent factors, ultimately leading to misleading conclusions in lead hazard assessments.