I'm translating a text where a 4-parameter dose-response log curve is fitted to experimentally obtained data. The text says:
The obtained dose-response curve (S-shaped) should contain points on the upper and lower plateaus and at least 4 points in the linear region and bending regions.
As I understand, there should be data points at the very top and the very bottom of the curve, and 4 data points belonging to the range that includes the "linear region" (where the curve goes at a slant linearly) and the two "bends".
Do they call them "bending regions", "bends" or "inflecting regions", "inflections" or something else?
Best Answer
These are the "knees" of the curve.
An exponential curve is self-similar, but it still has a "knee". The "knee of the curve" (of an exponential) is where it visually appears to change from being approximately horizontal to approximately vertical.
Mathematically, an S-curve is very similar to a pair of exponential curves joined at the S-curve's midpoint. Thus, it makes sense to call the transitions between the middle "linear" portion and the tails "knees".