(a) Curve with negative GRmax value corresponds to a cytotoxic response (cell death). (b) Curve with GRmax value converging to 0 corresponds to a cytostatic response (no growth). (c) Curve with positive GRmax value corresponds to a partial growth inhibition; GR50 is not defined as GRinf is above 0.5. (d) Noisy, weak response for which the sigmoidal fit is not significantly better than a flat fit, and thus GEC50 is set to 0 and GR50 is not defined. Hill slope, hGR, is defined in all but the last case, whereas the area over the curve (GRAOC) can always be calculated.