Which measure indicates a dose that has apparent effects on test subjects?

The measure that indicates a dose showing apparent effects on test subjects is the dose referred to as ED50. This is the effective dose at which 50% of the test population experiences a specified effect of the drug or substance being studied. ED50 provides valuable information about the potency of a compound and helps assess the dosage required for achieving a desired therapeutic effect without causing significant side effects.

The significance of ED50 lies in its ability to guide dosing in clinical and safety studies, allowing practitioners to establish effective and safe levels for treating patients or assessing risk in toxicology. For example, knowing the ED50 can aid in determining the right amount of a medication needed for a significant percentage of patients to experience relief from symptoms—critical in both clinical applications and research.

Other measures mentioned serve different purposes. LD50, for instance, indicates the lethal dose for half of the subjects, focusing on toxicity rather than therapeutic effects. TLV-STEL refers to threshold limit values that indicate safe exposure levels over short periods but does not specifically measure effectiveness. Therefore, ED50 is uniquely positioned as an important metric for understanding the dose-related effects of substances in biological systems.