Validity and reliability of clinical measurements are best described as:

• A. Validity describes accuracy; reliability describes repeatability or reproducibility.
• B. Validity describes precision; reliability describes accuracy.
• C. Validity and reliability both describe accuracy.
• D. Reliability describes bias; validity describes calibration.

Answer: (A)

Validity is about accuracy—the closeness of a measurement to the true value or the intended standard. Reliability is about repeatability or reproducibility—the extent to which repeated measurements under the same conditions produce the same result. For example, a blood pressure cuff that reads the true pressure is valid; if it gives the same reading on repeated measurements, it is reliable. A device can be highly reliable (consistent readings) but not valid if it’s biased and consistently off from the true value until properly calibrated. Conversely, a device could be valid on average but not reliable for individuals due to random variation. So, validity describes accuracy, while reliability describes repeatability or reproducibility.