Root cause

A root cause is an underlying cause that leads to an outcome or effect of interest. Commonly, root cause is used to describe the earliest event in the causal chain where an intervention could realistically have prevented the outcome.

Effects have causes. The causes may be natural or man-made, active or passive, initiating or permitting, obvious or hidden. Those causes that lead immediately to the effect are often called direct or proximate causes (see proximate causation). The direct causes often result from another set of causes, which could be called intermediate causes, and these may be the result of still other causes. When a chain of cause and effect is followed from a known end-state, back to an origin or starting point, root causes are found. The process used to find root causes is called root cause analysis.

The usual purpose of attempting to find root causes is to solve a problem that has actually occurred, or to prevent a less serious problem from escalating to an unacceptable level (see Near miss (safety), for example). The basic concept is that solving a problem by addressing root causes is ultimately more effective than merely addressing symptoms or direct causes. Consider the following example, where root cause $a$ leads to effect $e$, with a few intervening steps.

$a\to b\to c\to d\to e$

Assume each of these factors is as described below:

• $e$: car will not start
• $d$: battery is dead
• $c$: alternator does not function
• $b$: alternator is well beyond its designed service life
• $a$: car is not being maintained according to recommended service schedule

The effect, $e$, could be prevented by addressing any of the other factors. For example, attaching jumper cables from another car (addressing factor $d$) will probably allow the problem-car to be started. However, this solution is not likely to provide long-lasting relief from the undesired effect, as factor $c$ will ensure that the car shuts down again in a very short period of time. Addressing factor $c$ by repairing the alternator may solve the problem for a longer period, but factor $b$ will eventually result in another age-related breakdown in the alternator. The alternator could be replaced with a new unit, addressing factor $b$, thus allowing the car to be driven for an extended period of time. However, factor $a$ will eventually ensure that the car breaks down again for some other reason. Clearly, the best solution to the problem (and many other potential problems) is to maintain the car properly, which addresses factor $a$, the root cause.

An issue closely related to solving an existing problem is to foster learning that will embed knowledge (within a person, group, or organization) that may help prevent similar problems from occurring in the future. Such knowledge is often referred to as lessons-learned. Gaining such knowledge, retaining it, and using it effectively is one of the goals of a learning organization engaged in continuous improvement.

There is little agreement as to the types of conditions that can reasonably be considered root causes. One view holds that, in theory, one would have to return to the Big Bang or the point of Creation (theology) to find true root causes. An alternate viewpoint is that one need only consider factors within the boundary of the system that exhibits the problem. The former is usually used as one argument against attempts to single out specific factors as root causes, while the latter (or some version of it) is usually proposed as a practical bound within which useful information can be obtained.

Practitioners of root cause analysis often define what the phrase "root cause" means for a particular setting and application. The benefits of finding deeper layers of root cause tend to diminish after a certain point. The practical application of root cause analysis therefore often searches only as long as the benefit of answers outweighs the effort of the search.