Introduction to Analytical Measurement Uncertainty

This online course introduces the topic of measurement uncertainty and defines the basic terms of measurement. The reason that all measurements contain some level of doubt is explained and illustrated. A distinction is made between random and systematic error and examples are given. The importance of understanding measurement uncertainty in a laboratory setting is stated and examples are provided of situations in which the laboratorian will need this knowledge. The mathematical functions used in calculating standard deviation are demonstrated and the role of standard deviation in determining measurement uncertainty is explained. Finally, the user is taken, step by step, through the calculations necessary to determine the uncertainty of a laboratory sample, using an example from an environmental chemistry laboratory.

Throughout the course, graphics, photographs and narration are employed to provide the user with an interesting and informative experience. Additionally, the course includes printable training aids and an interactive section to engage the user and also reinforce the lessons. This course provides a basis for those new to the subject of measurement uncertainty and a refresher for laboratorians who would like to review the basics.


Course Level

This is a basic, entry level course.

No prior knowledge of the subject is necessary to participate in this course.


Intended Audience

This course is useful for all laboratory staff who perform testing that requires the determination of measurement uncertainty or standard deviation.


Learning Objectives

After completion of this course, the participant will be able to:

• Identify measurement as a comparison with some known standard.

• Define terms commonly used to express measurement in laboratory settings.

• Discuss the difference between precision and accuracy in measurement.

• Estimate the precision of a measurement by computing a standard deviation.

• Describe key tools or methods used to evaluate or estimate uncertainty. 

• Identify benefits of proficiency in calculating measurement uncertainty.



APHL would like to acknowledge the contribution of the following person in development of this course.


Marcia Valbracht

Quality Assurance Engineer

BS, Education


Certified Facilitator, emphasis on the adult learner

State Hygienic Laboratory at The University of Iowa



Estimation of Uncertainty of Measurement, Appendix G. Retrieve on March 31, 2012 from AIHA-LAP, LLC at

Guidelines for Uncertainty Estimation. Retrieve on March 31, 2012 from AIHA-LAP, LLC at

Guidance on the Estimation of Uncertainty of Measurement. Retrieve on March 31, 2012 from AIHA-LAP, LLC at

Interpretation and Guidance of the Estimation of Uncertainty of Measurement in Testing. Asian Pacific Laboratory Accreditation Cooperation (APLAC) TC 004, Issue No. 3, Dec. 2006


Introducing the Concept of Uncertainty of Measurement in Testing in Association with the Application of the Standard ISO/IEC 17025. ILAC-G17:2002.

k = 2 and Other Sometimes Hidden Assumptions in Chemical Measurement Uncertainty Interval.  Duewer, David L. et al. Simposio de Metrologia, Oct. 2006.

Measurement Good Practice Guide No. 11 (Issue 2): A Beginner’s Guide to Uncertainty of Measurement. Bell, Stephanie, Centre for Basic, Thermal and Length Metrology National Physical Laboratory, Teddington, Middlesex, UK, 1999.



• Any external link provides additional information that is consistent with the intended purpose of APHL's site.

• APHL cannot attest to the accuracy of these sites.

• Linking to these sites does not constitute an endorsement by APHL or any of its employees of the sponsors or the information and products presented on the site.

• You will be subject to the destination site's privacy policy when you follow the link.