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Root Cause Analysis Methods Compared

If you are evaluating the various Root Cause Analysis methodologies you can find a comprehensive comparison of all method types in Comparison of Common Root Cause Analysis Tools and Methods.

Comparison Criteria

If we are to evaluate the many so-called root cause analysis methods and tools, we need a standard to which they can be compared. It is generally agreed that the purpose of root cause analysis is to find effective solutions to our problems such that they do not recur. Accordingly, an effective root cause analysis process should provide a clear understanding of exactly how the proposed solutions meet this goal.

To provide this assurance, an effective process should meet the following six criteria:

  1. Clearly defines the problem and its significance to the problem owners.  
  2. Clearly delineates the known causal relationships that combined to cause the problem.  
  3. Clearly establishes causal relationships between the root cause(s) and the defined problem.  
  4. Clearly presents the evidence used to support the existence of identified causes.  
  5. Clearly explains how the solutions will prevent recurrence of the defined problem.  
  6. Clearly documents criteria 1 through 5 in a final RCA report so others can easily follow the logic of the analysis.

Various RCA Methods and Tools in Use Today

As you will discover in this analysis, there is a clear distinction between an RCA method and a tool. A tool is distinguished by its limited use, while a method may involve many steps and processes and has wide usage. (More...)

Realitycharting*

(Method) A simple causal process whereby one asks why of a defined problem, answers with at least two causes in the form of an action and condition, then asks why of each answer and continues asking why of each stated cause until there are no more answers. At that time, a search for the unknown is launched and the process is repeated several times until a complete cause and effect chart, called a Realitychart, is created showing all the known causes and their inter-relationships. Every cause on the chart has evidence to support its existence or a “?” is used to reflect an unknown and thus a risk. All causes are then examined to find a way to change them with a solution that is within your control, prevents recurrence, and meets your goals and objectives. The result is clear causal connections between your solutions and the defined problem. Because all stakeholders can see these causal relationships in the Realitychart, buy-in of the solutions is readily attained.

* A note on terminology: What we used to call “Apollo Root Cause Analysis” is being replaced by the term “Realitycharting.” The end result, a Realitychart, is being requested by name. Informed managers require Realitycharts for all major problems and employees ask to be trained because they see how it can help them be more successful. Realitycharting has become a core competency in many companies because the return on investment is overwhelmingly positive.

Events and Causal Factors Charting

(Method) A complicated process that first identifies a sequence of events and aligns them with the conditions that caused them. These events and respective conditions are aligned in a time-line. Events and conditions that have evidence are shown in solid lines but evidence is not listed; all others are shown in dashed lines. After this representation of the problem is complete, an assessment is made by “walking” the chart and asking if the problem would be different if the events or conditions were changed. This leads to causal factors that would then be evaluated using a tree diagram (discussed below).

Change Analysis

(Tool) A six-step process that describes the event or problem; then describes the same situation without the problem, compares the two situations and writes down all the differences; analyzes the differences and identifies the consequences of the differences. The results of the change analysis is the cause of the change and will frequently be tied to the passage of time and, therefore, easily fit into an Events and Causal Factors Chart, showing when and what existed before, during and after the change. Change analysis is nearly always used in conjunction with an RCA method to provide a specific cause, not necessarily a root cause. 

Barrier Analysis

(Tool) An incident analysis that identifies barriers used to protect a target from harm and analyzes the event to see if the barriers held, failed, or were compromised in some way by tracing the path of the threat from the harmful action to the target. A simple example is a knife in a sheath. The knife is the threat, the sheath is the barrier, and the target is a human. If the sheath somehow fails and a human is injured, the barrier analysis would seek to find out why the barrier failed. The cause of this failure is then identified as the root cause.

Tree Diagrams

(Method) This type of root cause analysis is very common and goes by many names such as Ishikawa Fishbone Diagram, Management Oversight and Risk Tree Analysis (MORT), Human Performance Evaluations System (HPES), and many other commercial brands. These methods use a predefined list of causal factors arranged like a fault tree.

They are sometimes called “Pre-Defined Fault Trees.” The American Society for Quality (ASQ) and others often call these categorical methods “Cause-and-Effect Diagrams.” All categorization methods use the same basic logic. The premise is that every problem has causes that lie within a pre-defined set of categories. Ishikawa uses Manpower, Methods, Machinery’ and Environment as the top-level categories. Each of these categories has sub-categories and sub-sub-categories. For example, within the category of Manpower, we may find Management Systems; within Management Systems we may find Training; and within Training we may find Training Less Than Adequate; and so on. These methods ask you to focus on one of the categories such as People and in reviewing what you know of your event choose some causal factors from the pre-defined list provided. Each categorical method has its own list of causal factors. After reviewing the list for each category, you are asked to vote on which causal factors most likely caused your problem. After some discussion, the most likely ones are voted on and called root causes. Solutions are then applied to these “root causes” to prevent recurrence. Each commercial brand has a different definition of root cause, but it is generally a cause that you are going to attach a solution to that prevents recurrence. Some of these methods refer to themselves as “Expert Systems” and also provide pre-defined solutions for your problems.

Why-Why Chart

(Method) One of many brainstorming methods also known as the “Five-Whys” method. This is the most simplistic root cause analysis process and involves repeatedly asking “why” at least five times or until you can no longer answer the question. Five is an arbitrary figure. The theory is that after asking “why” five times you will probably arrive at the root cause. The root cause has been identified when asking “why” doesn’t provide any more useful information. This method produces a linear set of causal relationships and uses the experience of the problem owner to determine the root cause and corresponding solutions.

Pareto Analysis

(Tool) A statistical approach to problem solving that uses a database of problems to identify the number of pre-defined causal factors that have occurred in your business or system. It is based on the Pareto principle, also known as the 80-20 rule, which presumes that 80% of your problems are caused by 20% of the causes. It is intended to direct resources towards the most common causes. Often misused as an RCA method, Pareto analysis is best used as a tool for determining where you should start your analysis.

Story Telling Method

(Method) This is not really a root cause analysis method but is often passed off as one, so it is included for completeness. It is the single most common incident investigation method and is used by nearly every business and government entity. It typically uses predefined forms that include problem definition, a description of the event, who made a mistake, and what is going to be done to prevent recurrence. There is often a short list of root causes to choose from so a Pareto chart can be created to show where most problems come from.

Fault Tree Analysis

(Method) Fault Tree Analysis (FTA) is a quantitative causal diagram used to identify possible failures in a system. It is a common engineering tool used in the design stages of a project and works well to identify possible causal relationships. It requires the use of specific data regarding known failure rates of components. Causal relationships can be identified with “and” and “or” relationships or various combinations thereof. FTA does not function well as a root cause analysis method, but is often used to support an RCA. More later.

Failure Modes and Effects Analysis

(Tool) Failure Modes and Effects Analysis (FMEA) is similar to fault tree analysis in that it is primarily used in the design of engineered systems rather than root cause analysis. Like the name implies, it identifies a component, subjectively lists all the possible failures (modes) that could happen, and then makes an assessment of the consequences (effect) of each failure. Sometimes a relative score is given to how critical the failure mode is to the operability of the system or component. This is called FMECA, where C stands for Criticality.