Accuracy and Precision

Two concepts that are often confused are accuracy and precision.  The following graphs illustrate the difference between these ideas.
  • Accuracy of a sample is how close the sample mean (xbar) is to the population mean (mu).
  • Precision of a sample is how much confidence one may have in the estimated sample mean. This is based on the dispersion of the sample points.
Figure 1 Figure 1

Figure 1 - The sample estimate is both accurate and precise. Distribution view and target view.

Figure 2 Figure 2

Figure 2 - The sample estimate is accurate but less precise. Distribution view and target view.

Figure 3 Figure 3

Figure 3  - The sample estimate is biased but just as precise as figure 1. Distribution view and target view.

Also See:

Chapter 1 - Introduction pages 1-6 in:

Zar, J. H. 2007. Biostatistical Analysis. Prentice-Hall, Inc. Englewood Cliffs, New Jersey. 718 pp.


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Natural Resources Biometrics by David R. Larsen is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License .

Author: Dr. David R. Larsen
Created: August 16, 1998
Last Updated: December 12, 2019