1.8
Accuracy and Precision
Scientists typically make repeated measurements of a quantity to ensure the quality of their findings and to evaluate both the precision and the accur…
Scientists make repeated measurements of a quantity during experimentation to ensure that their results are accurate and precise.
The accuracy of a measurement is the degree of closeness of the results to the true or accepted value.
Consider two students, A and B, who repeatedly weighed a gold bar known to have a true mass of 10 grams. Students A and B each reported three values from repeated measurements of the gold bar. Student A reported values closer to the true mass of the bar compared to student B. Thus, measurements by student A were, therefore, more "accurate".
Precision, on the other hand, is the measure of how closely the results agree with each other, or how reproducible they are.
A measurement is said to be precise if it gives highly similar results when repeated under the same conditions.
For instance, the values for the mass of the gold bar reported by student B were very similar to one another, as compared to student A. That is "precision".
Accuracy and precision are two distinct qualities of measurement which are independent of each other. Thus, a particular set of measurements can be either accurate, or precise, or neither, or both.
Highly accurate values tend to be precise too. Like a weighing balance showing true or close to true masses for all of the objects, repeatedly. However, highly precise measurements may not necessarily be accurate - if the same balance is improperly calibrated, it may give precise but inaccurate readings. This may lead to scientific errors.
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Q1: What is the difference between accuracy and precision in scientific measurements?
Accuracy measures how close results are to the true or accepted value, while precision measures how closely results agree with each other when repeated. A measurement can be accurate without being precise, precise without being accurate, or both. For example, an improperly calibrated balance may give precise but inaccurate readings, leading to scientific errors.
Q2: Why do scientists make repeated measurements of a quantity?
Repeated measurements allow scientists to evaluate both the precision and accuracy of their results, ensuring data quality. By comparing multiple measurements taken under the same conditions, scientists can determine whether their measurements are reproducible and close to the true value, which is essential for reliable experimental findings.
Q3: Can a measurement be precise but not accurate?
Yes. Highly precise measurements may not necessarily be accurate. An improperly calibrated thermometer or faulty weighing balance may consistently give similar readings that are far from the true value. This demonstrates that precision alone does not guarantee accuracy, and both qualities must be evaluated independently.
Q4: What does it mean for measurements to be reproducible?
Reproducible measurements yield highly similar results when repeated under the same conditions, which defines precision. If a measurement is reproducible, it demonstrates that the experimental procedure is consistent and reliable, though this does not guarantee the results are close to the true value.
Q5: How are accuracy and precision related in highly accurate measurements?
Highly accurate values tend to be precise too. A well-calibrated weighing balance, for example, repeatedly shows true or close-to-true masses for all objects measured. However, this relationship is not guaranteed in reverse; precision does not always imply accuracy without proper calibration and validation.
Q6: What scientific errors can result from improperly calibrated instruments?
Improperly calibrated instruments may produce precise but inaccurate readings, creating systematic errors in experimental data. These measurements appear consistent and reproducible, but deviate from the true value. This can lead to incorrect conclusions and compromised research quality if not detected through comparison with known standards.
Q7: How do you determine if a set of measurements is both accurate and precise?
Compare repeated measurements to both each other and to a known true or accepted value. If measurements cluster closely together and near the true value, they are both precise and accurate. Using rules for significant figures in calculations helps maintain measurement quality throughout data analysis and interpretation.