Root Cause

A root cause is rarely an initiating cause of a causal chain which leads to an outcome or effect of interest. Commonly, root cause is misused to describe the depth in the causal chain where an intervention could reasonably be implemented to change performance and prevent an undesirable outcome.

In plain English a "root cause" is a "cause" (harmful factor) that is "root" (deep, basic, fundamental, underlying or the like).

The term root cause has been used in professional journals as early as 1905, but the lack of a widely accepted definition after all this time indicates that there are significantly different interpretations of exactly what constitutes a root cause.

Many governmental investigation agencies avoid the term or use it informally. Others use it in a stilted formalistic or bureaucratic manner. The National Transportation Safety Board, with an excellent investigative reputation, uses the term "probable cause." (In law enforcement "probable cause" has a very different meaning.)

A common view of "root cause" follows.

Every adverse effect is the result of a set of direct factors, the absence of any one of which would have resulted in the effect having been different than it was.

Each of these direct factors was the result of deeper direct factors.

If the probing goes deep enough one finds harmful factors that deserve the designation "root cause."

Once an investigation gets to one or more root causes it is good practice to check the work with the following queries:

1. What are the other harmful factors that have equal or better claim to be called "root causes?"
2. For each of those "root causes" what are the factors that directly resulted in the "root cause" as described? Is it still a "root cause?"

The two biggest differences in viewpoint regard the possibility of an outcome having more than one root cause.