Q1(a). Accuracy and precision

Answer in brief

Accuracy is the closeness of a result (or of the mean) to the true or accepted value; precision is the closeness of replicate results to one another.

Key points

• Accuracy: the degree of agreement between the measured value (or the mean of replicates) and the true or accepted value.
• Accuracy is expressed as absolute error E = x̄ − μ or relative error; it is lowered by determinate (systematic) errors.
• Precision: the degree of agreement among replicate measurements of the same quantity (repeatability, reproducibility).
• Precision is expressed as standard deviation, relative standard deviation, variance, range or confidence interval; it is governed by indeterminate (random) errors.
• Good precision does not guarantee accuracy: high precision is a necessary but not sufficient condition for accuracy.