On a linear, non-threshold dose-response curve, where does the curve intersect the x-axis (dose axis)?

On a linear, non-threshold dose-response curve, where does the curve intersect the x-axis (dose axis)?

• A. At the origin
• B. At the threshold
• C. Midline at the average gradient
• D. Between the abscissa and ordinate

Answer: (A)

In a linear, non-threshold dose-response, the effect is directly proportional to the dose and there is no minimum dose needed to produce an effect. That means the relationship can be described by a line that passes through the origin, so when the dose is zero, the response is zero. Therefore, the curve intersects the dose axis exactly at the origin. If there were a threshold, the crossing would occur at a positive dose, but in this model there is no such threshold—the line starts at zero on both axes.

In a linear, non-threshold dose-response, the effect is directly proportional to the dose and there is no minimum dose needed to produce an effect. That means the relationship can be described by a line that passes through the origin, so when the dose is zero, the response is zero. Therefore, the curve intersects the dose axis exactly at the origin. If there were a threshold, the crossing would occur at a positive dose, but in this model there is no such threshold—the line starts at zero on both axes.