nondetection

Nondetection refers to the absence of detection of a signal, object, or event during an observation or measurement, even when the thing being sought may be present or detectable under ideal conditions. It is the complement of detection and is a fundamental consideration in many technical and scientific contexts.

In analytical measurement and monitoring, nondetection occurs when an analyte's concentration is at or below the method's limit of detection. A nondetect result does not prove absence; it indicates that the available signal is too weak to be distinguished from noise with the specified method.

In signal processing and detection theory, outcomes include hits, misses, false alarms, and correct rejections. Nondetection typically corresponds to a miss (present signal not detected) or, in some contexts, to a correct rejection (no signal detected when none is present). The rates of nondetection influence assessments of sensitivity and reliability.

In radar, sonar, and other remote sensing applications, nondetection arises when a target fails to register due to distance, attenuation, clutter, limited resolution, or adverse environmental conditions. Improving system sensitivity or data integration can reduce nondetection probability.

In ecological, epidemiological, and surveillance surveys, nondetection is common because observers may miss a present species or event. Statistical approaches that model detection probability separately from occupancy or true state help avoid bias and improve estimates of true presence.