Comparatively Speaking: Precision vs. Accuracy in Formulating

Tony O'Lenick explains the difference between precision and accuracy as it relates to formulating.

Raw materials are designed by suppliers to follow a set of specifications that product developers can use to make purchasing decisions. These specifications should indicate that the raw material is the same from batch to batch. In dealing with numbers, the reliability and reproducibility of these values become important. Two important concepts related to the quality of the numbers but defining different aspects are accuracy and precision.

Accuracy is a term that relates to how close a value is to the real and desired value, while precision relates to how well the values can be reproduced in a series of tests. The best analogy is target shooting. The bull’s eye is the real value. If a one shoots the bull’s eye, they are accurate; the further the shot is away from the bull’s eye, the less accurate it is. If one shoots several times, the average may well be accurate but the variation of each shot from the bull’s eye determines the precision.

Accuracy is a measure of how close a series of numbers comes to the hitting the bull's eye. Precision is a measure of how well each independent shot varies from one another. This is important in analytical chemistry since a raw material specification cannot be tighter than the precision of the tests. A practical example is retesting the same samples over and over and finding in some cases, they are within specifications while in others, they are not.

This difference is important not only to raw material suppliers as they set material specifications, but also to formulators using these materials since there can be some variance among samples. Potential material variations should be considered when building formulations and completed formulations should be tested to ensure performance.

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