1. UNDERSTANDING HUMAN ERROR Text p. 366

2. What order of actions occurs when receiving money from an ATM?

3. Types of Error Action Taken Yes No Intended? Error of Omission Lapse MistakeSlip Violation: the intentional taking of a wrong action with full awareness

4. Slips Automatic and subconscious You have the right goal and the right intention, but take the wrong action Often come from skilled behaviour – why?

5. Why Skilled Behaviour creates Errors With skill, behaviours automatic Automatic behaviour is adaptive and efficient But less conscious processing allows slips

6. Mode Error A specific kind of slip People forget the mode the system is in Take the right action in the wrong mode

7. Mistakes Inappropriate goals or intentions Poor decisions Misunderstanding the situation Not taking all of the relevant factors into account

8. Why do Mistakes Happen? Humans use experience and heuristics to make decisions Not logical or rational Very efficient … but prone to error

9. Types of Mistakes Mistaken Similarity Misjudged Probability Rationalizing small events Social pressures, cultural factors and $

10. Mistaken Similarity Similarity to a previous situation makes people think this is the same situation I’ve seen this before Rapid conclusion without all the information

11. Misjudged Probability People estimate rare events are more likely than they are Gamblers

12. Rationalizing Small Events Explain away small events as normal A chain of small events creates a large problem

13. Social, Cultural $ Pressure to take risks Reluctance to confront authority figures who are making mistakes

14. Counteracting Human Error Minimize or don’t use modes Make sure different objects look different Make dangerous actions hard or impossible to do Make actions reversible Make errors obvious

15. Which is the best approach to take and why?

16. Adopting the Right Attitude Use mistakes to improve your design Ask why did it occur? How can I improve the design to eliminate it? Assume the person making the mistake was right

17. Design using Forcing Functions What is a forcing function? A forcing function constrains action so that mistakes can not occur

18. Why people work with designs that cause errors People tend to accept their errors and blame themselves. “I’m not smart enough, I’m a klutz” People will create explanations of their world, right or wrong. “I can’t run these two things at the same time.” When people work with your designed object they WILL develop a theory of how and why it works. “Hit it on the side.” YOU need to ensure that that theory is correct.