A Review of the Similarities and Difference Between 5 Whys and Fishbone Diagrams

A Review of the Similarities and Difference Between 5 Whys and Fishbone Diagrams
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5-Why is a method of analysis that explores cause and effect relationships to delve into the root cause of a problem. The methodology entails asking questions on the cause of underlying symptoms, and asking further questions on the answer, to probe at a deeper level. The number “five” is arbitrary, based on the assumption that asking “Why?” to the order of five usually provides the ultimate root cause. The name notwithstanding, there is no hard and fast rule to limiting to five levels of questions.

Assume a problem as customers having to wait at check out counters of a supermarket, for long periods on the first week of the month. The apparent cause of the problem is lack of adequate cash counters to handle peak hour risk, or poorly trained cash clerks. A 5-Why analysis however identifies something different as the root-cause. This approach requires asking a question “why do customers have to wait long at cash counters during the first week of the month.” The answer could be “because of more customers patronizing the store at this time.” This leads to the next question “why do customers patronize the store more during the first week.” The answer, which may require a customer survey, could be “availability of quality products and competitive prices.” This leads to the next question “why are quality products at competitive prices available on the first week.” The answer, derived from a qualitative study on the store could lie in the company strategy of stocking up new products, offering discounts, and going for advertisements at the start of the month to attract salaried customers, and customers understanding the fact and trying to maximize purchase at the start of the month to get a better deal.” This is the root cause of the problem. Possible solutions could include spreading out offers and promotions across the month, but that does not come under the purview of the 5-Why analysis.

Fishbone Diagram

The Fishbone diagram, also known as the Cause-and-Effect diagram or Ishikawa diagram is a tool to identify and present all the possible causes of a particular problem grouped into categories, in a systematic and graphical format. The diagram represents the bone structure of a fish. A box at the head contains the statement of the problem. The spine or the main line has different branches for different categories of problems, and each branch has different boxes, to list specific issues or problem. Each box can branch outward, and with each branch, the level of detail increase, and the outermost branch usually identifies the root cause of the problem.

Although there is no hard and fast rule regarding the number or nature of branches, many manufacturing related fishbone diagrams use five branches for ‘Man’, ‘Machine’, ‘Materials’, ‘Methods, and ‘Measurement’, while others use 8 P’s, for “Procedures,” “People,” “Price,” “Promotion,” “Processes,” “Plant,” “Product,” and “Policies.” Or the 4 S’s of “Skills,” “Surroundings,” “Systems,” and “Suppliers.”


The difference between 5-whys and fishbone diagrams remain limited to the mode of execution, and very often, fishbone diagrams serve as effective means to apply 5-whys. Each branch and subsequent sub-branches finds use to collate all the “whys” of different orders or levels of probing, in an easy to understand “snap shot” or illustrative format. This allows decision makers and problem solvers to focus attention of these whys and identify the root cause rather than digress into the symptoms or history of the problem.

Both 5-Why and fishbone diagram require brainstorming or mind-mapping techniques to explore causes of a problem. Such brainstorming invariably involves several rounds of discussions to identify the causes, causes for such “causes” and so on, until the people involved cannot think of any further sub-causes.

Completing the fishbone leads to analysis, to identify the root cause from the various causes identified. In the example of the supermarket cited above, the possible root causes for excessive rush on the first week of the month might be company policy of targeting promotions and advertisements during this month, the company’s system of taking in fresh stock, or the simple fact that people get their salaries and have purchasing power at that time. There can be more than one “root cause,” and in the example above, all these factors may work in tandem, and the company would have to address all possible issues to solve the problem.


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