Five whys (or 5 whys) is an
iterative
Iteration is the repetition of a process in order to generate a (possibly unbounded) sequence of outcomes. Each repetition of the process is a single iteration, and the outcome of each iteration is then the starting point of the next iteration. ...
interrogative
technique used to explore the
cause-and-effect
Causality (also referred to as causation, or cause and effect) is influence by which one event, process, state, or object (''a'' ''cause'') contributes to the production of another event, process, state, or object (an ''effect'') where the ca ...
relationships underlying a particular problem. The primary goal of the technique is to determine the
root cause of a
defect
A defect is a physical, functional, or aesthetic attribute of a product or service that exhibits that the product or service failed to meet one of the desired specifications. Defect, defects or defected may also refer to:
Examples
* Angular defec ...
or problem by repeating the question "Why?" five times. The answer to the fifth why should reveal the root cause of the problem.
The technique was described by
Taiichi Ohno
was a Japanese industrial engineer and businessman. He is considered to be the father of the Toyota Production System, which inspired Lean Manufacturing in the U.S. He devised the seven wastes (or muda in Japanese) as part of this system. He ...
at
Toyota
is a Japanese multinational automotive manufacturer headquartered in Toyota City, Aichi, Japan. It was founded by Kiichiro Toyoda and incorporated on . Toyota is one of the largest automobile manufacturers in the world, producing about 10 ...
Motor Corporation. Others at Toyota and elsewhere have criticized the five whys technique for various reasons (see ).
Example
An example of a problem is: The vehicle will not start.
#''Why?'' – The
battery
Battery most often refers to:
* Electric battery, a device that provides electrical power
* Battery (crime), a crime involving unlawful physical contact
Battery may also refer to:
Energy source
*Automotive battery, a device to provide power t ...
is dead. (First why)
#''Why?'' – The
alternator
An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current. For reasons of cost and simplicity, most alternators use a rotating magnetic field with a stationary armature.Go ...
is not functioning. (Second why)
#''Why?'' – The alternator
belt
Belt may refer to:
Apparel
* Belt (clothing), a leather or fabric band worn around the waist
* Championship belt, a type of trophy used primarily in combat sports
* Colored belts, such as a black belt or red belt, worn by martial arts practit ...
has broken. (Third why)
#''Why?'' – The alternator belt was well beyond its useful service life and not replaced. (Fourth why)
#''Why?'' – The vehicle was not maintained according to the recommended service schedule. (Fifth why, a root cause)
The questioning for this example could be taken further to a sixth, seventh, or higher level, but five
iteration
Iteration is the repetition of a process in order to generate a (possibly unbounded) sequence of outcomes. Each repetition of the process is a single iteration, and the outcome of each iteration is then the starting point of the next iteration. ...
s of asking why is generally sufficient to get to a root cause. The key is to encourage the trouble-shooter to avoid assumptions and logic traps and instead trace the chain of causality in direct increments from the effect through any layers of abstraction to a root cause that still has some connection to the original problem. Note that, in this example, the fifth "why" suggests a broken process or an alterable behavior, which is indicative of reaching the root-cause level.
The last answer points to a process. This is one of the most important aspects in the five why approach – the ''real'' root cause should point toward a process that is not working well or does not exist. Untrained facilitators will often observe that answers seem to point towards classical answers such as not enough time, not enough investments, or not enough resources. These answers may be true, but they are out of our control. Therefore, instead of asking the question ''why?'', ask ''why did the process fail?''
History
The technique was originally developed by
Sakichi Toyoda
was a Japanese inventor and industrialist. He was born in Kosai, Shizuoka. The son of a farmer and sought-after carpenter, he started the Toyoda family companies. His son, Kiichiro Toyoda, would later establish Japan's largest automaker, Toyo ...
and was used within the
Toyota
is a Japanese multinational automotive manufacturer headquartered in Toyota City, Aichi, Japan. It was founded by Kiichiro Toyoda and incorporated on . Toyota is one of the largest automobile manufacturers in the world, producing about 10 ...
Motor Corporation during the evolution of its manufacturing methodologies. It is a critical component of problem-solving training, delivered as part of the induction into the
Toyota Production System
The Toyota Production System (TPS) is an integrated socio-technical system, developed by Toyota, that comprises its management philosophy and practices. The TPS is a management system that organizes manufacturing and logistics for the automobile ma ...
. The architect of the Toyota Production System,
Taiichi Ohno
was a Japanese industrial engineer and businessman. He is considered to be the father of the Toyota Production System, which inspired Lean Manufacturing in the U.S. He devised the seven wastes (or muda in Japanese) as part of this system. He ...
, described the five whys method as "the basis of Toyota's scientific approach by repeating why five times the nature of the problem as well as its solution becomes clear."
The tool has seen widespread use beyond Toyota, and is now used within
Kaizen
is concept referring to business activities that continuously improve all functions and involve all employees from the CEO to the assembly line workers. ''Kaizen'' also applies to processes, such as purchasing and logistics, that cross organ ...
,
lean manufacturing
Lean manufacturing is a production method aimed primarily at reducing times within the production system as well as response times from suppliers and to customers. It is closely related to another concept called just-in-time manufacturing ( ...
,
lean construction Lean construction is a combination of operational research and practical development in design and construction with an adoption of lean manufacturing principles and practices to the end-to-end design and construction process. Unlike manufacturing ...
and
Six Sigma. The five whys were initially developed to understand why new product features or manufacturing techniques were needed, and was not developed for root cause analysis.
In other companies, it appears in other forms. Under
Ricardo Semler
Ricardo Semler (born 1959) is the CEO and majority owner of Semco Partners, a Brazilian company best known for its radical form of industrial democracy and corporate re-engineering. Under his ownership, revenue has grown from 4 million US dollars ...
,
Semco
Ricardo Semler (born 1959) is the CEO and majority owner of Semco Partners, a Brazilian company best known for its radical form of industrial democracy and corporate re-engineering. Under his ownership, revenue has grown from 4 million US dollars ...
practices "three whys" and broadens the practice to cover
goal setting
A goal is an idea of the future or desired result that a person or a group of people envision, plan and commit to achieve. People endeavour to reach goals within a finite time by setting deadlines.
A goal is roughly similar to a purpose or a ...
and
decision-making
In psychology, decision-making (also spelled decision making and decisionmaking) is regarded as the Cognition, cognitive process resulting in the selection of a belief or a course of action among several possible alternative options. It could be ...
.
Techniques
Two primary techniques are used to perform a five whys analysis:
* the
fishbone (or Ishikawa) diagram
* a
tabular format
These tools allow for analysis to be branched in order to provide multiple root causes.
Criticism
The five whys have been criticized as a poor tool for root cause analysis. Teruyuki Minoura, former managing director of global purchasing for Toyota, criticized them as being too basic a tool to analyze
root causes to the depth that is needed to ensure that they are fixed.
Reasons for this criticism include:
* Tendency for investigators to stop at symptoms rather than going on to lower-level root causes.
* Inability to go beyond the investigator's current knowledge – the investigator cannot find causes that they do not already know.
* Lack of support to help the investigator provide the right answer to "why" questions.
* Results are not repeatable – different people using five whys come up with different causes for the same problem.
* Tendency to isolate a single root cause, whereas each question could elicit many different root causes.
Medical professor Alan J. Card also criticized the five whys as a poor root cause analysis tool and suggested that it be abandoned entirely.
His reasoning also includes:
* The artificial depth of the fifth why is unlikely to correlate with the root cause.
* The five whys is based on a misguided reuse of a strategy to understand why new features should be added to products, not a root cause analysis.
To avoid these issues, Card suggested abandoning the five whys and instead use other root cause analysis tools such as
fishbone
Fishbone is an American rock band formed in Los Angeles in 1979, that plays a fusion of ska, punk, funk, metal, reggae, and soul. AllMusic has described the group as "one of the most distinctive and eclectic alternative rock bands of the lat ...
or lovebug diagrams.
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See also
* Eight disciplines problem solving
* Five Ws
The Five Ws (sometimes referred to as Five Ws and How, 5W1H, or Six Ws) are questions whose answers are considered basic in information gathering or problem solving. They are often mentioned in journalism (''cf.'' news style), research, and poli ...
(information-gathering)
* Four causes
The four causes or four explanations are, in Aristotelian thought, four fundamental types of answer to the question "why?", in analysis of change or movement in nature: the material, the formal, the efficient, and the final. Aristotle wrote th ...
* Issue map
The issue-based information system (IBIS) is an argumentation-based approach to clarifying wicked problems—complex, ill-defined problems that involve multiple stakeholders. Diagrammatic visualization using IBIS notation is often called issue ...
* Issue tree
An issue tree, also called logic tree, is a graphical breakdown of a question that dissects it into its different components vertically and that progresses into details as it reads to the right.
Issue trees are useful in problem solving to ide ...
* Root cause analysis
In science
Science is a systematic endeavor that builds and organizes knowledge in the form of testable explanations and predictions about the universe.
Science may be as old as the human species, and some of the earliest archeologic ...
* Socratic method
The Socratic method (also known as method of Elenchus, elenctic method, or Socratic debate) is a form of cooperative argumentative dialogue between individuals, based on asking and answering questions to stimulate critical thinking and to draw ...
* Why–because analysis
Why–because analysis (WBA) is a method for accident analysis. It is independent of application domain and has been used to analyse, among others, aviation-, railway-, marine-, and computer-related accidents and incidents. It is mainly used as an ...
References
External links
"Dauerspezial" commercial of Deutsche Bahn, where the question "why" is posed 5 times (in German)
{{Lean Manufacturing Tools
Problem solving methods
Lean manufacturing