graded response
Imagine turning up a dimmer switch: the light does not just flip on, it grows brighter and brighter as you rotate the dial. A graded response works the same way. As you give an individual more and more of a drug, the size of the effect grows smoothly and continuously, rather than jumping from nothing to everything.
Formally, a graded response is measured in a single biological system — one person, one isolated muscle strip, one cell culture — where the variable being watched can take any value along a continuous scale, such as heart rate, blood pressure, or millimetres of muscle contraction. Plot the magnitude of that effect against dose and you get the familiar hyperbolic dose–response curve, which becomes an S-shape when dose is plotted on a logarithmic axis.
Graded responses are how we read off potency (the dose for a half-maximal effect) and efficacy (the maximum achievable effect) for that system. The key contrast is with the quantal response, which counts how many individuals in a population cross a yes/no threshold rather than measuring how strongly one individual reacts.
Increasing doses of the loop diuretic furosemide produce progressively larger urine volumes in one patient — a textbook graded response read from a single individual.
One person, a continuous output that rises with dose.
Graded and quantal curves can look almost identical when plotted, which trips up beginners. The difference is the y-axis: graded plots a continuous magnitude in one system, quantal plots the cumulative percentage of a population responding.