What is human error?
‘The human element is the most flexible, adaptable and valuable part of the … system, but it is also the most vulnerable to influences which can adversely affect its performance’.
(ICAO circular 216-AN/131, 1989)
Error is an ever-present and natural part of life and it is generally accepted that we will all make errors on a daily basis. Each of us already have an intuitive understanding of the term human error, but it is useful to define it in order to better understand its nature and to develop mechanisms for effective error management.
Human error is a generic term that involves all those instances where a planned activity fails to achieve its intended outcome. For example, forgetting to set your park brake in your car or misapplying your vehicle brakes in wet and slippery road conditions.
In any organisation, human error is a regular occurrence. The good news is that most of the time, these errors are self-corrected and they have little consequence. Other interesting facts about error include:
- Average rate of error is constant at 1-3 per hour whatever the expertise (except for beginners).
- Errors tend to decrease in more demanding situations (due to cognitive control) but the recovery rate collapses (due to insufficient mental capacity).
- Errors change with the nature of expertise. Routine based errors (slips & lapses) increase with expertise, knowledge base (mistakes) decrease.
- Motor skill errors (learning) are more frequent for beginners but decrease with experience.
- Experts are characterised by their ability to recover from error (anticipation).
 Reason, J. (1990). Human error. New York: Cambridge University Press.
What causes human error?
‘To err is human; to blame it on the other guy is even more human.’
Bob Goddard, rocket scientist
There are many reasons why human error occurs; it is not typically just one single factor. A summary of the main reasons found across a range of different industries can be grouped according to the following four broad areas:
- Human performance limitations (information processing capability, memory, fatigue, stress).
- Task or Environmental demands (time pressure, adverse weather).
- Organisational/Systemic factors (equipment design, poor management oversight, poor planning).
- Social and Cultural factors (peer pressure, group conformity, safety culture).
Errors are not random events. Rather, they are a consequence of what normally goes on in our mind, arising because of inattention, incomplete knowledge, sparse sensory data, mis-perceptions, forgetting something, problems in our relationships with colleagues, friends and family, and so on (see below Panel: Errors are consequences – not causes).