88: People Make Predictable Type of Errors

88: People Make Predictable Type of Errors

• In addition to thinking about the consequence of errors, as in the Van der Linen study described, there is another usual error taxonomy. The Morrell taxonomy classifies two types of errors: performance and moto-control.
• Performance Errors
• Performance errors are mistakes you make when you've gone through the steps to complete a procedure.
• Commission Errors
• Taking additional steps that were unnecessary
• Omission Errors
• You've only set up the outgoing ones. In this case, you omitted steps.
• Wrong-Action Errors
• You took an action at the appropriate point in the procedure, but it was the wrong action.
• Moto-Control Errors
• Motor-control errors are those you make while using the controls of a device.
• You may have different errors that you want to track as you design or conduct user testing.
• The important thing is to decide ahead of time which types of errors you think people will make, and which are important for you to detect and correct.

The Swiss Cheese Model of Human Error

• James Reason wrote that errors have a cumulative effect.
• It starts with an error in the organization, which then leads to additional errors in supervision, which leads to even more errors. Each error makes a hole in the system until the end when you have Swiss cheese (lots of holes), eventually leading to a human error that is a mishap.
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• Bildunterschrift: The Swiss Cheese Model

The Human Factors Analysis and Classification Sys

• Scott Shappell and Douglas Wiegmann wrote a paper on HFACS for the U.S. Office of Aviation Medicine. They focused on preventing errors in aviation, such as pilot error and control tower error.
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• Bildunterschrift: HFACS Flow Chart

Takeaway

• People will make different types of errors in learning about and using your product. Before you conduct user testing or user observation, decide on the possible errors you are most concerned about.
• During user testing and observation, collect data on which category of errors people are making. This will help focus your redesign efforts after testing.
• If you’re in a field where errors are not just annoying or inefficient, but actually may result in accidents or loss of human lives, then you should use a system like HFACS to analyze and prevent errors.