Human Error

1. Introduction

○ ○ To err is human, to forgive is the role of the computer interface ○ Norman (1988) in “The Psychology of Everyday Things” If an error is possible, someone will make it. The designer must assume that all possible errors will occur and design so as to minimize the chance of the error in the first place, or its effects once it gets made. Errors should be easy to detect, they should have minimal consequences, and, if possible, their effects should be reversible.

2. Classifying Human Error

1) 2) ○ the state of believing what is untrue  cognitive aspect something incorrectly done  physical aspect actions & consequences of the actions 1. Human Error Categories 1.

phenomenological classification – phenotype or error forms 2.

classification on causes – genotype or error type U SER I NTERFACE L ABORATORY

Human Error

Classification by consequences ○ the superficial nature of error or the error manifestation ○ ‘how’ rather than ‘why’ the error happened Classification by underlying causes ○ cognitive mechanism involved or cognitive biases 2. Slips and Mistakes ○ ○ ○ at the level of intention or planning correct plan but wrong action – slips – failures of execution wrong plan and correct action – mistakes – planning failure ○ ○ ○ ○ Reason (1990) based on SRK-behavior (Rasmussen, 1986) skill-based slips – SATO, intrinsic variability of operators rule-based mistakes -- wrong rules, incorrect recall, interference knowledge-based mistakes – resource limitations U SER I NTERFACE L ABORATORY

Human Error

3. Cognitive Control & System Error Mechanisms ○ Rasmussen and Vicente (1987) 1.

2.

Errors related to learning and adaptation Errors due to interference among competing cognitive control structures 3.

4.

Errors due to lack of resources Errors due to intrinsic human variability 4. Error-Shaping Factors (

Table 1 )

3. Error Capture and Recovery

○ the classic 80-20 rule for error-free interface design ○ to design an interface which is free of errors 80% of the time takes 20% of the overall design time Not justifiable because of money U SER I NTERFACE L ABORATORY

Human Error

U SER I NTERFACE L ABORATORY

Human Error

System Response to Human Error ○ six possible responses (Lewis and Norman, 1995) (1) Gag (prevent user from continuing, (2) Warn (beeps), (3) Do Nothing (4) self-correct, (5) Let’s talk about it, and (6) Teach me Error Messages ○ not only tells the user what went wrong but also provides some information on how to take the right action ○ Eberts (1994) -- lacking in feedback effetiveness, unfriendly Feedback – facilitates error recovering

4. Error Reduction: Issues and Guidelines

○ R & V (1987) – guidelines of dealing with errors 1. Avoiding Mode Error ○ reduce the number of modes or totally eliminated U SER I NTERFACE L ABORATORY

Human Error

2. Maintaining Consistency ○ the concept of consistency implies that the mechanisms should be used in the same way wherever and whenever they occur ○ lack of consistency in the command structure – description errors 3. Facilitating Multiple Activities ○ human errors because of limitations of memory and environmental disruption ○ ○ two aspects – levels of cognitive control and levels of attention cognitive control 1) conscious control – performance of novel tasks, rule-based or knowledge-based level of control 2) unconscious or sub-conscious control – skill-based behavior (well practiced routine tasks) U SER I NTERFACE L ABORATORY

Human Error

○ ○ Attention -- limits of selective, focused and divided attention when multiple activities are significant (Miyata & Norman, 1986) ○ systems should be easy to suspend an activity ○ ○ sufficient info should be saved with the suspended task a reminding structure should be available 4. KIH vs. KIW ○ ○ ○ ○ ○ KIW in the task components reduces the load on human memory KIW through design aids, memory checklists, cue cards, etc.

KIH rely on the users’ memory – Miller (1956) recognition rather than recall KIW – unaesthetic, time consuming, impossible due to physical constraints but makes the system easy to use ○ KIH – more efficient and aesthetic but errors due to memory loss, recall problems, more time to learn U SER I NTERFACE L ABORATORY

Human Error

5. Knowledge about users ○ all ages with varying levels of experience; different cultural backgrounds and some have disabilities ○ people with disabilities – 1/10 hearing impairment, 1/125 deaf, 1/100 visual disability 6. Understanding Cultural Biases ○ Silverman (1992) – cultural biases, cultural motivation, and missing knowledge as possible causes for mistakes ○ Yeo (1996) – cultural user interface (CUI) ○ ○ overt factors – tangible and easily observed covert factors – metaphors, colors, sounds are intangible 7. Generating Appropriate Interface Metaphors U SER I NTERFACE L ABORATORY

Human Error

7. Selecting Interface Icons ○ the design of icons carefully analyzed as they can lead to errors ○ semantic – the relationship of a visual image to a meaning  well does this symbol represent the message?

how ○ syntactic – the relationship of one visual image to another  does this icon look and related to other icons?

how ○ pragmatic – the relationship of visual image to a user  symbol be seen and does it remain visible?

can the 8. Use of Colors ○ with great care by location, size, shape of the area it fills, surrounding colors, external conditions, physiological and cultural differences among individuals U SER I NTERFACE L ABORATORY

Human Error

10. On-Line Help ○ help system predicated on (Roesler and Mclellan, 1995) 1) information needs – help items and types 2) help access methods – how to access help, what help where 11. Training

5. Designing for Error Tolerance

○ Rasmussen (1990), Senders and Moray (1991) ○ errors are inavoidable side effects – have a role in the development and maintaining of expertise ○ ○ an error-forgiving design features for an error-tolerance interface (Hollnagel, 1990)

6. Benefits of Reducing Error

○ increase user productivity, decrease training costs, user frustrations, & customer support U SER I NTERFACE L ABORATORY