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Uncertainty: Overview

Uncertainty: Overview

In analytical chemistry, we often perform repetitive measurements to detect and minimize inaccuracies caused by both determinate and indeterminate errors. Despite the cares we take, the presence of random errors means that repeated measurements almost never have exactly the same magnitude. The collective difference between these measurements - observed values - and the estimated or expected value is called uncertainty. Uncertainty is conventionally written after the estimated or expected value.

Uncertainty in Measurement: Accuracy and Precision

Uncertainty in Measurement: 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 accuracy of their results. Measurements are said to be precise if they yield very similar results when repeated in the same manner. A measurement is considered accurate if it yields a result that is very close to the true or the accepted value. Precise values agree with each other; accurate values agree with a true value.

Uncertainty: Confidence Intervals

Uncertainty: Confidence Intervals

The confidence interval is the range of values around the mean that contains the true mean. It is expressed as a probability percentage. The interpretation of a 95% confidence interval, for instance, is that the statistician is 95% confident that the true mean falls within the interval. The upper and lower limits of this range are known as confidence limits. The confidence limits for the true mean are estimated from the sample's mean, the standard deviation, and the statistical factor 't,' or...

Accuracy and Precision

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 accuracy of their results. Measurements are said to be precise if they yield very similar results when repeated in the same manner. A measurement is considered accurate if it yields a result that is very close to the true or the accepted value. Precise values agree with each other; accurate values agree with a true value. Highly accurate measurements...

Accuracy and Precision

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 accuracy of their results. Measurements are said to be precise if they yield very similar results when repeated in the same manner. A measurement is considered accurate if it yields a result that is very close to the true or the accepted value. Precise values agree with each other; accurate values agree with a true value. Highly accurate measurements...

Uncertainty in Measurement: Reading Instruments

Uncertainty in Measurement: Reading Instruments

Counting is the type of measurement that is free from uncertainty, provided the number of objects being counted does not change during the process. Such measurements result in exact numbers. By counting the eggs in a carton, for instance, one can determine exactly how many eggs are there in the carton. Similarly, the numbers of defined quantities are also exact. For example, 1 foot is exactly 12 inches, 1 inch is exactly 2.54 centimeters, and 1 gram is exactly 0.001 kilograms. Quantities...

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Updated: Jun 28, 2026

Split Point Analysis and Uncertainty Quantification of Thermal-Optical Organic/Elemental Carbon Measurements

Split Point Analysis and Uncertainty Quantification of Thermal-Optical Organic/Elemental Carbon Measurements

Published on: September 7, 2019

Accuracy profiles from uncertainty measurements.

A Gustavo González¹, M Angeles Herrador

¹Department of Analytical Chemistry, University of Seville, Spain.

|October 31, 2008

Summary

Accuracy profiles, derived from analytical result uncertainty, are introduced for chemical assays. This method uses measurement uncertainty estimation from validation data, illustrated with a quinine determination case study.

Area of Science:

Analytical Chemistry
Chemical Metrology

Background:

Accurate chemical analysis is crucial for reliable results.
Quantifying uncertainty is essential for understanding assay reliability.

Purpose of the Study:

Introduce and define accuracy profiles for chemical assays.
Demonstrate the calculation and application of accuracy profiles using validation data.

Main Methods:

Deriving accuracy profiles from analytical result uncertainty.
Estimating measurement uncertainty from assay validation data.
Spectrofluorimetric determination of quinine in tonic water as a case study.

Main Results:

Accuracy profiles provide a comprehensive assessment of assay performance.

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The method allows for clear visualization of assay accuracy across a range of analyte concentrations.

The case study successfully illustrates the practical application of accuracy profiles.

Conclusions:

Accuracy profiles offer a robust framework for evaluating chemical assay performance.
This approach enhances the interpretation of analytical results by incorporating measurement uncertainty.
The spectrofluorimetric determination of quinine demonstrates the utility of accuracy profiles in real-world applications.