Definition
Plain language
A pattern where almost nothing happens, then things change suddenly, then the effect levels off.
As stated in the literature
A sigmoidal/logistic response profile with a flat low region, a steep transition around a threshold, and a saturating ceiling; characteristic of threshold-crossing dynamics rather than gradual drift.
Also called: S-curve, S curve, sigmoidal, logistic curve
Why it matters: If a behaviour follows this shape, testing at low doses tells you almost nothing about what happens just past the tipping point, so safety evaluations that stop short of the transition can look reassuring and be wrong.
For example, adding clues about a person's identity to a conversation may change nothing for the first several clues, then flip the model into answering as that person almost all at once, after which more clues make little difference.