Which statement accurately defines the relative standard deviation (RSD)?

• A. It is the ratio of standard deviation to the mean expressed as a percentage.
• B. It is the slope of the calibration curve.
• C. It is the intercept of the standard curve.
• D. It is the mean value of measurements.

Answer: (A)

The concept being tested is how to quantify precision relative to the size of the measurement. Relative standard deviation expresses variability as a percentage of the mean, calculated by dividing the standard deviation by the mean and multiplying by 100. This gives a unitless value that lets you compare how precise results are across different conditions or methods, since the spread is scaled to the average result. It’s the same idea as the coefficient of variation. It’s not about the slope or intercept of a calibration curve, and it’s not simply the mean value. One caveat: if the mean is very small or near zero, the RSD can become large or misleading, so interpretation should consider the context.