8.9.6 Measurement Uncertainty And Decision Rules

Every reported result should include an uncertainty evaluation appropriate to the assessment. Under AS/NZS 2772.2, all reported assessments of measured or calculated RF field levels must include an uncertainty estimate. Unless a client or regulator specifies otherwise, the standard calls for a one-sided 95% coverage interval with an upper bound for a compliance assessment and a two-sided 95% coverage interval for an environmental assessment. Potential contributions include calibration, frequency response, isotropy or antenna pattern, linearity, noise and resolution, cable and mismatch corrections, detector response, temporal and spatial sampling, positioning, source variability, extrapolation, and environmental perturbation.

The assessment should also state the decision rule used when comparing the result with a limit. In the absence of an externally specified rule, AS/NZS 2772.2 uses the upper bound of a one-sided 95% coverage interval and provides uncertainty allowances of 3 dB for reference levels and 1.2 dB for basic restrictions. When the upper-bound uncertainty exceeds the applicable allowance, the excess is added to the best estimate before comparison with the limit. A conservative screening method may justify a proportionate uncertainty evaluation when the result is well below the criterion, but it does not justify omitting the estimate.

Small differences between readings should not be treated as meaningful when they are within the combined measurement uncertainty or normal source variability. The conclusion should be supported by the measured or calculated result, its uncertainty, and the stated decision rule rather than by the displayed reading alone.