From The Ergoweb® Learning Center

Validity of Ergonomic Risk Assessments

The most widely used ergonomic assessment tools in industry are risk assessment checklists such as RULA, REBA, and the Washington State checklist. These can be completed in a fairly short period of time by a person with a reasonable amount of training. They are intended to identify jobs or tasks that result in WMSD hazard exposures, and in some cases, to provide a basis for prioritizing ergonomic challenges.

One element to consider in evaluating different ergonomic risk assessments is the question of validity. Validity, in simple terms, is the extent to which a tool measures what it is intended to measure. For example, a meat thermometer is valid if you get medium-well steak when the instrument tells you the temperature is in the right range for medium-well. For ergonomic risk assessments, three questions to consider are:

  • Is the methodology based on sensible, logical reasoning (face validity)?

  • Are the results consistent with accepted methods (correlation validity)?

  • Do WMSD injury rates increase as risk scores increase (predictive validity)?

Face Validity
Is the methodology based on sensible, logical reasoning?  For ergonomic risk assessments, verify that the tool references risk factors that are consistent with NIOSH’s review of MSDs and workplace factors (published in 1997) or the National Academy of Science review of the same issue (published in 2001). Risk factor types and threshold values should be consistent with these reports.

One example of face validity violation is combining visual factors such as poor lighting with WMSD risk factors such as high forces and awkward postures. While lighting and visual factors are important to ergonomics, poor lighting has not been shown to increase the risk of WMSDs and therefore does not fall under the category of “risk factors”.

Correlation Validity
Are the results consistent with accepted methods?  While no industry standards have been adopted, the Washington State hazard checklist (available from is based on scientific research and was constructed to withstand intense review. This tool may become the “gold standard” to which other risk assessments can be compared.

While other approaches to risk assessment may be as effective or more so than the Washington State tool, it is good practice to ensure that jobs and tasks that are deemed hazardous with this tool are deemed hazardous by the alternative tool. Just as important, jobs and tasks that are deemed not hazardous should also be deemed not hazardous by the alternative tool.

Predictive Validity
Do WMSD injury rates increase as risk scores increase?  This is the holy grail of risk assessment validity

This article originally appeared in The Ergonomics Report™ on 2002-08-01.