Human error is behavior that is wholly expected to achieve a desired result (in accordance with some standard) but that does not. A causal factor is anything that yields an occurrence resulting in an undesired effect or anything that exacerbates the level of severity of the undesired effect.

Why is it important to understand human error causal factors? The answer is twofold.

First, a good design (either the design of a process or hardware item) is created, in large part, with an understanding of:

1. Any potential undesired effects in operating or maintaining the process or in manufacturing, transporting, storing or using the hardware item
2. The human errors and their causal factors that can activate these undesired effects.

With this understanding, the intent is to design such as to eliminate the potential for the undesired effects, or when that can’t be done, to establish appropriate barriers for the:

1. Prevention of any error that could activate the undesired effect
2. Timely detection of the error
3. Mitigation of the undesired effect.

Of course, the resources applied to any such barriers are appropriate to the level of significance of the undesired effect.

Second, without an understanding of human error causal factors, there is a greater potential for root cause analyses to be truncated at the point at which only the things that need correction are identified, rather than analyzing further to the point of identifying the behaviors that need correction as well. For example, a correction may be made to a specific integrated maintenance and inspection plan (a thing) or corrections may be made to a set of such plans (things) that have the same or similar offending characteristics, but such a correction or corrections will not prevent newly prepared plans from having the same or similar offending characteristics. Improvement in new plans can come about only with improvement in the behavior of the planners.

The table, below, provides a taxonomy of universally applicable human error causal factors. This taxonomy was devised from my review of hundreds, if not thousands of problem reports, incident reports, non-conformance reports, condition reports, and the like, as well as my participation in or review of many of the root cause analyses resulting from these reports.

I want to stress that these causal factors may or may not be root causes but, certainly, are closer to root causes than “things.”

A knowledge-based error may occur when one has not received the information, either because it wasn’t transmitted or got lost or garbled in its transmission or receipt.

A cognition-based error may occur when one does not properly process the information that one has received—does not properly memorize it, understand it, apply it, or in jobs requiring higher cognitive abilities, does not properly analyze it, synthesize it, or evaluate it.

There’s a significant difference between not having the information (knowledge-based) and not having the ability to process the information (cognition-based).

A cognition-based error is derived from the work of Benjamin Bloom (1913-1999), an educational psychologist who, in 1956, published a taxonomy describing the six levels of cognition that apply to learning (Taxonomy of Educational Objectives: The Classification of Educational Goals)

• Memorization—(Dr. Bloom called it “knowledge) is the most basic, first cognitive level. It is the ability to remember terminology, definitions, facts, ideas, materials, patterns, sequences, methodologies, principles, etc.
• Comprehension—The ability to understand the things listed in the first level of cognition, including tables, diagrams and other forms of communication that combine words and graphics.
• Application—In job-related situations, it is the ability to use the information and understandings acquired at the memorization and comprehension levels.
• Analysis or diagnosis—The ability to break-down information into its constituent parts; recognize the organizational and systemic relationships of the parts; and identify actual and potential part non-conformances, anomalies, and improvement opportunities.
• Synthesis—The ability to put parts together such as to show a pattern or structure that was not evident previously, identify the data that support conclusions, and identify data that are appropriate to examine further in order to form new solutions or methods.
• Evaluation—The highest and sixth cognitive level. It is the ability to make judgments regarding significance, value or worth, usually by using appropriate criteria or standards to estimate accuracy, effectiveness, economic benefits, etc.

Higher levels of cognition are needed to prevent errors. Higher levels of cognition also are needed to identify the existence and nature of problems arising from errors. There are two exceptions: The existence and nature of a problem may be so obvious as to be regarded as “low hanging fruit”, so to speak. And a problem may be “self-revealing”— i.e., the problem may be one that already has resulted in an occurrence for which the undesired effect has been experienced. For example, a component that is required to provide an output of 120 volts ± 5%, during functional test may provide an output of only 100 volts. The existence of the problem has revealed itself. However, much higher levels of cognition are required to determine the nature of the problem. Is it a design deficiency and, if so, specifically what kind of design deficiency, and why did it exist? Is it a manufacturing nonconformance and, if so, what kind of a manufacturing nonconformance, and why did it exist?

Designs are created for the:

1. Administrative processes used to govern how business is to be conducted, including how product is to be designed
2. Products, either hardware items, documents, service processes, or a combination of these
3. Technical or conversion processes used to convert computerized and hard copy design documents into the physical hardware items, and to maintain and operate the items.

In designing these things, tools should be used to enhance cognitive abilities for preventing errors and for detecting and correcting them and their causes prior to design release. These tools include failure mode and effects analysis and hazard-barrier-effects analysis, among others. Unfortunately, too often, the use of these tools is limited to after an “event” or “near miss” has occurred, with significant adverse consequences.

Continuing with the taxonomy:

A value-based error occurs when something is done knowingly in violation of the requirement, expectation, or need because the doer does not respect the requirement, expectation, or need, thinking it to be wrong or unnecessary in a given situation. In a rural flatland farming community, with very little traffic and excellent visibility, what percentage of the time would a conventional red and white, octagonal “STOP” sign at an intersection be ignored?

In large part, procedure noncompliance is due to value- or belief-based error. Sometimes the procedure is, in fact, wrong. Sometimes there should be an alternative option for a given situation. However, one would make an additional reflexive-based error by acting in noncompliance with the procedure, rather than stopping to get the procedure changed.

If a procedure was developed with the inputs of the process expert, other subject matter experts, users or representatives of the users, other experts involved with the “abilities” (e.g., workability), and a procedures writing expert, and if that procedure was used in training and given additional review at that point, and if, especially, that procedure was “qualified,” then willful noncompliance with the procedure is egotistical and in some cases dangerous. Techniques for the prevention of value-based error are mostly in the realm of culture.

A reflexive-based error may occur when one is presented with a condition or situation to which an immediate response or reaction is required and for which the required action is not procedurally specified. The operator has to do something and when that something is reflexive or reactive, the potential for error is greater. Fortunately, the benefits of procedure specificity can be achieved without losing procedure flexibility, but the techniques for that are also a topic for another time.

An error-inducing condition-based error may occur when an error-inducing condition exists and when one has not used the appropriate behaviors to counteract the condition. Some such conditions are inherent in the task, itself, some are in the environment in which the task must be accomplished, and some are in our human attributes. Many of these conditions cannot be designed out of the process or hardware because it would not be cost-effective or because the conditions are natural. Fortunately, there are dozens of behaviors that can be learned and practiced to counteract the dozens of these conditions.

No matter how practiced a worker, skill-based errors also will exist until the time that they are avoided by automation. For example, in manual welding, even with the utmost attention, slag occurs.

Humans are fallible. Therefore, lapse-based errors will exist until they are avoided by automation. When an individual makes lapse-based errors at an unacceptable frequency, they may have more specific root causes—e.g., a long-standing emotional problem, the use of medication, substance abuse, or attention deficit disorder.

As noted earlier, an understanding of human error causal factors is very important for process and hardware item design and root cause analysis. For the latter, it is very important to be able to identify the human errors that occur not only at the implementing operator level but, upstream, at the design levels, as well—and to recognize the classifications of such error in order to be able to correct the behaviors relating to these classifications. Anything less is ineffective.