Trick Question – What’s More Important: Measurement Precision or Accuracy?

Six Sigma Measurement Precision

The title revealed the trick question right away. Neither measurement precision nor accuracy have more value than the other in a general sense. But by now you may be asking yourself a couple more trick questions: “Aren’t accuracy and precision one in the same? How can one be more important than the other?”

General confusion about the meaning of accuracy and precision have led to the terms being used interchangeably in conversation. However, today we’ll dispel the myth that there’s no difference between the two and help you determine which result matters more to your measurement system.


Breaking Down the Definitions

Accuracy is used to assess just how well the average measurement of multiple measurements stacks up against the standard measurement of the same item or the true value. Precision can be viewed as a definition of how close various measurements are to each other. Essentially, both terms refer to measurements systems and possible errors, but are not truly interchangeable. Measurement systems can have errors and issues with both accuracy and precision.

There are two core parts to precision:

  1. Repeatability
  2. Reproducibility

Repeatability demonstrates a variation made when the same part is measured repeatedly with the same device and operator. Reproducibility is observed the same part is measured using the same drive by different operators.

As you may have gathered by this point, measurement accuracy and measurement precision are vital to determining the credibility or trustworthiness of your measurement system and by extension, its data.

To learn how to produce accurate and precise measurement systems, register for NWCPE’s Six Sigma program today.


Is Your Measurement System Accurate or Precise?

What makes a measurement system accurate? Once values have been observed and the mean determined, the mean should be close to the standard value for the system to be defined as accurate. For an easy recall of accuracy’s purpose, remember that is all about the mean of the data being observed.

Onto precision. A measurement system is precise when the values being observed fall near one and other. If the values fall within a greater distance from one and another, the measurement system does not demonstrate precision. To recall the purpose of measurement precision, remember the concept of standard deviation. The more standard deviation found among the data being observed, the less precise the measurement system is.

Master Measurement System Analysis in our upcoming module, SS 504.


The Implications of Inaccurate and Imprecise Measurements

It should be clear now that accuracy and precision are not one in the same. However, the value in discussing these terms extends beyond their definitions. Instead what matters are the implications of inaccurate and imprecise measurement.

To determine the implications, we must begin with the objective of the measurement. A simple, one-sized-fits-all answer will not suffice in this case. When observing the change in a process, keep your eye on precision. Accuracy matters when you are working to achieve a target.

Of course, there are occasions when both accuracy and precision matter. One of those scenarios would be when assessing if something complies with a tolerance. Both inaccurate and imprecise measurements can cause an inaccurate conclusion about said compliance.

Above, it is important to keep in mind that no measurement result can be marked as complete if it lacks an assessment. All measurements systems require accuracy and precision to generate measurements that are as close to the standard value and to one another as possible.

Ready to build accurate and precise measurements for Process Management and Improvement? Register for NWCPE’s Six Sigma Design of Experiments SS 505.