Which statement accurately describes graded versus quantal dose–response relationships?

Which statement accurately describes graded versus quantal dose–response relationships?

• A. Graded responses are continuous and relate to intensity; quantal responses relate dose to frequency.
• B. Graded responses are all-or-none and relate to frequency; quantal responses are continuous.
• C. Both are purely qualitative with no relation to dose.
• D. Both are identical in how they measure potency.

Answer: (A)

Graded and quantal dose–response relationships capture two different ways a drug’s effect changes with dose. A graded response looks at the magnitude of effect in a single subject or preparation. It is a continuous measure, so as you raise the dose the response changes smoothly in intensity rather than flipping on or off. A quantal response, on the other hand, looks at a population: for each dose, you record whether each individual responds or does not. You then plot the fraction or percent of individuals that respond at that dose, which describes frequency across the group and yields a sigmoid curve when plotted against dose. So the best description is that graded responses are continuous and relate to the magnitude of effect, while quantal responses relate dose to the frequency of responders in a population. The other ideas are inconsistent: graded responses aren’t all-or-none and don’t measure frequency in a single subject; quantal responses aren’t a continuous measure of intensity at the population level; and potency is assessed differently for the two, using different endpoints (magnitude measures for graded vs. fraction of responders for quantal).

Graded and quantal dose–response relationships capture two different ways a drug’s effect changes with dose. A graded response looks at the magnitude of effect in a single subject or preparation. It is a continuous measure, so as you raise the dose the response changes smoothly in intensity rather than flipping on or off. A quantal response, on the other hand, looks at a population: for each dose, you record whether each individual responds or does not. You then plot the fraction or percent of individuals that respond at that dose, which describes frequency across the group and yields a sigmoid curve when plotted against dose.

So the best description is that graded responses are continuous and relate to the magnitude of effect, while quantal responses relate dose to the frequency of responders in a population. The other ideas are inconsistent: graded responses aren’t all-or-none and don’t measure frequency in a single subject; quantal responses aren’t a continuous measure of intensity at the population level; and potency is assessed differently for the two, using different endpoints (magnitude measures for graded vs. fraction of responders for quantal).