In a linear-threshold dose-response model, what happens when the dose is at or below the threshold?

In a linear-threshold dose-response model, what happens when the dose is at or below the threshold?

• A. No effect
• B. Severity increases with dose
• C. Probability increases with dose
• D. Effects occur independent of dose

Answer: (A)

In this model, there is a definite dose level—the threshold—below which nothing happens. The idea is that the body can tolerate up to that point without showing any response. So when the dose is at or below the threshold, the expected effect is zero; no observable change occurs. Only when the dose exceeds the threshold does a response begin, and that response grows linearly with how much the dose surpasses the threshold. That’s why the option describing no effect at or below the threshold is the best choice. The other ideas—severity increasing with dose, probability increasing with dose, or effects occurring regardless of dose—imply a response starting from zero or independent of dose, which isn’t compatible with a linear-threshold relationship.

In this model, there is a definite dose level—the threshold—below which nothing happens. The idea is that the body can tolerate up to that point without showing any response. So when the dose is at or below the threshold, the expected effect is zero; no observable change occurs. Only when the dose exceeds the threshold does a response begin, and that response grows linearly with how much the dose surpasses the threshold.

That’s why the option describing no effect at or below the threshold is the best choice. The other ideas—severity increasing with dose, probability increasing with dose, or effects occurring regardless of dose—imply a response starting from zero or independent of dose, which isn’t compatible with a linear-threshold relationship.