Why “Human Error” Should Never Be an Assignable Root Cause


Devin I. McElroy, M.B.A, Sr. Director of Quality


Washington Osiro, M.B.A. (cand.), Director of Quality Engineering
Sormeh Mahjouri, M.P.H., Regulatory Manager


Are you frustrated by ineffective corrective actions and dealing with the same defects over and over again? The cause of many ineffective corrective actions are the assignment of “causes” that are not actually the root cause. For instance, assigning a root cause of “human error” will never lead to the prevention of repeat defects from human error in the future. The reason for this is that there are numerous reasons that humans will err. Human error is an established fact, not a root cause for the majority of defects in manufacturing. The reason for this is that the process itself allows human error to introduce defects. The most effective processes are those that eliminate human error as a variable by putting processes in place that make the process immune to human error. This white paper discusses how a thorough root cause investigation does not stop with an assignment of “human error” as a cause.

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In a greater than 25-year history working within medical device manufacturing, biotechnology, and pharmaceutical companies, there have been numerous times that I have witnessed root cause analysts assigning a root cause as “human error.” Since this is so prevalent in the industry, it was felt necessary to provide additional guidelines for the industry and root cause analysts to ensure that root cause investigations go above and beyond human error to determine the reason that the human erred. Many times, a root cause of human error may be assigned due to unfamiliarity with root cause analysis tools and techniques or unawareness of the need to develop processes that actually prevent human error from inattention, unknowledgeable workers, or intentional errors.

Root cause analysis is a requirement in the medical device, biotechnology, and pharmaceutical industries for complaints, nonconformances, and defects that require in-depth investigation to prevent recurrence of the same or similar failure originally identified. Although the regulations require root cause analyses, they do not provide any “good” or “bad” guidelines, systems or steps.

Ultimately, a root cause analysis should identify one or two causes that, if eliminated, would effectively eliminate all product defects that resulted from that cause or problem.


The problem with assigning “human error” as a root cause is that human error is a constant and, in and of itself, cannot be remediated. Humans will always err and a moment of inattention, distraction, or intention can result in a product defect. This product defect is actually caused by the lack of a process that obtains consistent results despite human error.

Even if one could make an argument that highly trained and retrained individuals are not likely to introduce significant errors in a given process, one must take into consideration the possibility of employees that would introduce errors intentionally. Disgruntled or apathetic employees can intentionally introduce error when the process is dependent on uncontrolled human interaction.

In addition, human error can occur in a process that changes frequently and when employees do not understand the process fully. This occurs in situations when the employee does not understand the procedure itself. For instance, the employee may not be fully fluent in the language that the procedure is written in and, therefore, they cannot read the procedures without assistance. This means that they cannot use the written procedures as reference materials when performing their job functions and have to go by memory alone. In addition, error can be introduced when a superior “tells” a line worker to do something differently than what is written, and they cannot understand the procedure.

Finally, environment itself can play a strong role in human error for manufacturing areas. Many manufacturing areas are open, noisy, busy places. For some individuals this environment may provide numerous interruptions to the smooth flow of work. Some processes are sensitive to interruption and, therefore, introduce human error through the various interruptions.

Ultimately, there are external and internal distractions, willful misconduct, and procedural issues that can impact a human’s capability for performing quality work and these issues themselves must be dealt with in order to prevent the human error in the first place.


When human error is found to be a contributory factor in product defects, proceed one step further and ask yourself the question, “Why did the human err?” This single question will lead to activities or items that can actually be corrected. Rewriting procedures in direct, command language makes procedures more understandable. Liberal use of diagrams or photographs can also help understanding. Finally, removing all extraneous information about “why” a process is being done can reduce confusion. If the “whys” for a process must be captured, put those in a procedure and keep only direct, command language in the work instruction.

Define, in your root cause analysis, the underlying reason that contributed to the human error such as “procedure not understandable,” “noisy environment,” “frequent interruptions,” “inability to access procedure,” “willful misconduct,” “unawareness of job processes on product quality,” “inaccessible tools,” and so on.

It is important that all root cause analysts are trained thoroughly to eliminate the assignment of “human error” in place of an actual root cause during product or complaint investigations. There are numerous tools and techniques available to assist in determining the triggering event for product defects and these should be appropriately applied and all analysts trained sufficiently to understand the use and application of these tools and techniques.


Neozene, as your analysis partner, has subject matter experts on staff that can perform thorough root cause investigations at your facility that apply and use the appropriate root cause analysis tools and methods of application that are best. In addition, Neozene employs a staff of subject matter experts and trainers that can provide your company with analysis tools and training that will ensure that your investigations are not only aligned with the regulatory requirements, but also reflect the industry best practices.


When “human error” is assigned as a cause in an investigation, going one step further and identifying the cause of the human error will result in more effective corrective actions and reduce recurrence of product defects. In addition, eliminating human error from the processes, which can be a significant contributory factor to variation, may also result in improved manufacturing throughput and lessen scrap and rework costs.

Author Biography

Devin is responsible for leading Neozene’s internal team of quality and regulatory subject matter experts. He has more than 25 years of experience in the medical device, biotechnology, and pharmaceutical industries as a Quality and Regulatory professional. Devin earned his Bachelor’s Degree in Business Information Systems and an MBA in Technology Management from University of Phoenix late in his career. He is currently pursuing his PhD in Business with a focus on Root Cause Analysis at Capella University and plans to graduate by December 2017.

To discuss your specific needs or issues and to have more in-depth technical discussions about the services that Neozene offers, send an email to Devin and his team at TE@neozene.com or call the main office at (510) 746-8693 and set up an appointment.