NoThreshold

Nothreshold is a cross-disciplinary term describing a relationship in which there is no distinct threshold separating zero or baseline response from a meaningful response to input. A threshold ordinarily marks the input level at which an effect becomes detectable or clinically relevant; nothreshold implies that any nonzero input could, in principle, produce some degree of response, even if arbitrarily small.

Applications appear in perception and signal processing as a theoretical or practical descriptor: most real systems show some threshold, but models may assume a continuous response starting at zero. In toxicology and risk assessment, nothreshold contrasts with threshold models: the linear no-threshold (LNT) model posits that no exposure is entirely risk-free and that risk increases linearly with dose, whereas threshold models assume a safe exposure below a certain level (NOAEL/LOAEL).

In other contexts, such as engineering or data analysis, the term is used more loosely to describe algorithms or processes that do not incorporate a fixed cutoff, instead handling inputs across a continuum; the precise interpretation depends on the field and model used. Related concepts include threshold, linear no-threshold models, and dose–response relationships.