Jan 18, 2010

Human Error Performance Modes and Error Reduction Tools

SKILL BASED ERRORS - Skill based errors are defined as a repetitive behavior performed many times. The probability of this type of error is 1:10,000.

Example: arriving at home, but being unable to remember the drive back from work.
RULE BASED ERRORS - Rule based errors are typically associated with misclassification of situations leading to the application of wrong rule or with the incorrect recall of procedures. The probability of a rule based error is 1:1,000.

Example: Calculate the square root of 74527?

KNOWLEDGE BASED ERRORS Knowledge based errors arise from resource limitations or incomplete or incorrect knowledge. The probability of a knowledge based error is 1:2.

Example: What’s the population of Trenton, NJ?

How do you keep your “brain in the game” and stay out of skill, rule, or knowledge based performance errors?

Use a Mental Model – This is a structured understanding of knowledge (e.g., what a system contains, how components work as a system, current state of system). Use frequent time outs or reminders to keep your mental model up to date.

Challenge Assumptions – This improves mental models, assists at problem solving and optimizes team performance.

Don’t take short cuts – Humans tend to seek order and patterns they recognize. Mental short cuts offer the human mind unconscious methods to create order. Personnel should be aware of the potential for error this creates during problem solving and decision making.

Make Conservative Decisions – Be cautious of what is truly important – safety! This attitude should be protected regardless of current schedule or production pressures. When you recognize conditions that could challenge safety, put components in a safe condition and seek prompt assistance.

Experience has shown that days following a holiday season are prime time for human performance errors. Stay in the prevention mode by utilizing your human performance tools, every day, for every task. Do not underestimate the difficulty or complexity of a task based on past experiences. We are in Knowledge Based Performance Mode More Often Than We Realize!!! Remember, You Don’t Know What You Don’t Know.


  1. Ken, this is an excellent description for everything I ever knew about safe driving. I can see how it applies to many things in life.


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  3. I had a typo and wanted to do my comment over.

    I try to keep my brain in the game but some days I'm concerned that I can't remember how I got from A to B while driving.

  4. Since I've cut back working at my trade (accounting, yawn) I find that I have gotten "less sharp". In fact, more than once my lovely husband has told me I've become kind of...well, stupid in some ways. I know it is due to not being mentally stimulated as I used to be. At this rate I'll be a babbling idiot in 5 years. :0

  5. Dear Ken, thanks for making comment son my blog for Christmas! I'm so glad that you and Beth had a great time!I hope that you will come by and comment on what you what from the new year and Haiti!
    Ken these milestones are marvelous! I wish that people from many disciplines would sue them!
    thanks for telling us about them! Hugs to you and Beth!


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