The Cause-Effect Diagram is a way of organizing and representing the different theories proposed about the causes of a problem. It is also known as the Ishikawa diagram (by its creator, Dr. Kaoru Ishikawa, 1943), or Fishbone diagram and is used in the Diagnosis and Solution phases of the cause.
Dr. Kaoru Ishikawa (father of total quality)
Professor Dr. Kaoru Ishikawa was born in Japan in 1915 and passed away in 1989. He graduated from the Department of Engineering at the University of Tokyo. He obtained a Doctorate in Engineering from said University and was promoted to Professor in 1960. He obtained the Deming Prize and a recognition from the American Quality Association. He died in 1989.
Dr. Kaoru Ishikawa - 1915-1989
He was the first author to attempt to highlight the differences between Japanese and Western management styles. Forerunner of the concepts of total quality in Japan. Later it had a great influence on the rest of the world, since it was the first to highlight cultural differences between nations as an important factor in achieving success in quality. He was highly convinced of the importance of the philosophy of the eastern peoples.
Ishikawa was interested in changing the way people think about their work. For him, quality was a constant process that could always be taken one step further. Today he is known as one of the most famous "gurus" of world quality. All those who are interested in the issue of quality should study Ishikawa, but not only superficially, reviewing his ideas, but deeply analyzing his conception of work and, above all, applying it to his own environment.
Quality control, a term so used today in all academic circles, was an approach of Ishikawa, more than 50 years ago, in post-war Japan. Quality control in a few words was defined by him as "Developing, Designing, Manufacturing and Maintaining a quality product". It is possible that Ishikawa's most important contribution has been its role in developing a Japanese quality strategy. He did not want company managers to focus only on product quality, but on the quality of the entire company, even after the purchase. He also preached that quality should be carried beyond the job itself, into daily life.
He was the founder of the Union of Japanese Scientists and Engineers (UJSE), an entity that was concerned with promoting quality within Japan during the post-war era.
Ishikawa made many contributions, among which are:
- Creation of the cause-effect diagram, or Hishikawa's fishbone, or in English “Fishbone Diagram” Demonstrated the importance of the 7 quality tools. Worked in quality circles.
His conceptual conception when conceiving his Cause-Effect Diagram (Ishikawa Fishbone) can be summarized in that when the analysis of a problem of any nature is carried out and not only related to health, they always have various causes of different importance, transcendence or proportion. Some causes may be related to the presentation or origin of the problem and others, with the effects it produces.
The Ishikawa diagram helps to graph the causes of the problem being studied and to analyze them. It is called "Fishbone" because of the way each of the causes or reasons that are understood to cause a problem are placed. It has the advantage that it allows to visualize in a very fast and clear way, the relationship that each of the causes has with the other reasons that affect the origin of the problem. Sometimes they are independent causes and in others, there is an intimate relationship between them, which may be acting as a chain.
The best way to identify problems is through the participation of all the members of the work team in which you work and get all the participants to state their suggestions. The concepts that people express will be placed in different places. The result obtained will be an Ishikawa Thorn Diagram.
Devised in 1953, it includes the following elements:
The main problem to be analyzed, which is placed on the far right of the diagram. It is advisable to enclose it in a rectangle for easy viewing.
The main causes that we believe have caused the problem.
Graphically it is constituted by a horizontal central axis that is known as "main line or central spine". It has several inclined arrows that extend to the central axis, to which they reach from its lower and upper part, depending on where the problem that is being analyzed or decomposed into its own causes or reasons has been placed. Each of them represents a group of causes that affect the existence of the problem. Each of these arrows in turn are touched by smaller arrows that represent the "secondary causes" of each "cause" or "group of causes of the problem".
The Diagram that is carried out must have very clearly written the name of the problem analyzed, the date of execution, the area of the company to which the problem belongs and you can even put additional information such as the name of those who have executed it, etc.
Key elements of Ishikawa's thought:
- Quality begins with education and ends with education. The first step to quality is knowing what the customer requires. The ideal state of quality is when inspection is not necessary. You have to remove the root of the problem, not the Symptoms. Quality control is the responsibility of all workers. Do not confuse means with objectives. First put quality and then put long-term profits. Trade is the in and out of quality. High Company executives should not be envious when a worker gives a valuable opinion. Problems can be solved with simple tools for analysis. Information without dispersal information is false information.
Ishikawa's theory was to manufacture everything at low cost. He postulated that some effects within companies that are achieved by implementing quality control are the reduction of prices, lower costs, establish and improve the technique, among others.
It is not in vain that Ishikawa is owed much gratitude for his ideas that revolutionized the world of industry, administration, commerce and services. Japan was nourished by its ability and its theories and became what we all see today.
How to interpret a cause-effect diagram?
The Cause-Effect diagram is a vehicle to order, in a very concentrated way, all the causes that are supposed to contribute to a certain effect.
It allows, therefore, to achieve a common knowledge of a complex problem, without ever being a substitute for the data. It is important to be aware that cause-effect diagrams present and organize theories. Only when these theories are contrasted with data can we prove the causes of observable phenomena.
Common mistakes are constructing the diagram before globally analyzing the symptoms, limiting the proposed theories by unintentionally masking the root cause, or making mistakes in both the causal relationship and the order of theories, assuming significant time expense.
Next we will see how the value of a quality characteristic depends on a combination of variables and factors that condition the production process (among other processes).
The example is based on the mayonnaise manufacturing process, to explain the Cause-Effect Diagrams:
The variability of quality characteristics is an observed effect that has multiple causes. When a problem occurs with the quality of the product, it should be investigated in order to identify its causes. To make a Cause-Effect Diagram the following steps are followed:
It is decided what will be the quality characteristic to be analyzed. For example, in the case of mayonnaise it could be the weight of the filled jar, the density of the product, the percentage of oil, etc.
A thick arrow representing the process is drawn and to the right the quality characteristic is written:
The most important and general causal factors that can generate the fluctuation of the quality characteristic are indicated, drawing secondary arrows towards the main one. For example: Raw Materials, Equipment, Operators, Measurement Method, etc.:
More detailed factors that can be considered causes of fluctuation are incorporated in each branch. To do this, you can ask these questions:
- Why is there fluctuation or dispersion in the quality characteristic values? Due to the fluctuation of Raw Materials. Raw Materials are listed as one of the main branches. Which Raw Materials produce fluctuation or dispersion in the values of the quality characteristic? Oil, Eggs, salt, other seasonings. Oil is added as a minor branch of the main branch. Raw Materials. Why is there fluctuation or dispersion in the oil? Due to the fluctuation of the quantity added to the mixture. We add to Oil the smallest branch Quantity. Why is there variation in the added amount of oil? Due to irregular operation of the balance. The Balance branch is registered. Why does the balance work irregularly? Because it needs maintenance. In the Balance branch we place the Maintenance branch.
Thus, the Cause-Effect Diagram continues to be expanded until it contains all possible causes of dispersion.
Finally, it is verified that all the factors that may cause dispersion have been incorporated into the diagram. The Cause-Effect relationships must be clearly established and in that case, the diagram is finished.
A Cause-Effect diagram is in itself educational, it serves to give people a deep understanding of the process they are working with, clearly visualizing the relationships between the Effects and their Causes.
It also serves to guide discussions, clearly exposing the origins of a quality problem. And it allows you to find more quickly the assignable causes when the process deviates from its normal operation.
PARETO CHART
The Pareto Diagram is a graph in which various data classifications are arranged in descending order, from left to right by means of simple bars after the data has been collected to classify the causes. So that an order of priorities can be assigned.
The name Pareto was given by Dr. Joseph Juran in honor of the Italian economist Vilfredo Pareto (1848-1923) who carried out a study on the distribution of wealth, in which he discovered that the minority of the population owned most of wealth and the majority of the population owned the least of the wealth. With this he established the so-called "Pareto Law" according to which economic inequality is inevitable in any society.
Dr. Juran applied this concept to quality, obtaining what is known today as the 80/20 rule.
According to this concept, if you have a problem with many causes, we can say that 20% of the causes solve 80% of the problem and 80% of the causes only solve 20% of the problem.
Therefore, Pareto Analysis is a technique that separates the "vital few" from the "trivial many". A Pareto chart is used to graphically separate the significant aspects of a problem from the trivial ones so that a team knows where to direct their efforts to improve. Reducing the most significant problems (the longest bars on a Pareto Chart) will serve more of an overall improvement than reducing the smallest. Often, one aspect will have 80% of the problems. In the rest of the cases, between 2 and 3 aspects will be responsible for 80% of the problems.
Using the Pareto Diagram, the most relevant problems can be detected by applying the Pareto principle (few vital, many trivial), which says that there are many minor problems versus only serious ones.
The graph is useful in allowing to visually identify in such a review such minorities of vital characteristics to which it is important to pay attention and in this way use all the necessary resources to carry out corrective action without wasting effort.
In relation to the management styles of Problem Solving and Decision Making, it can be seen how the use of this tool can be an excellent alternative for a Firefighter style manager, who constantly when solving problems only "extinguishes fires", that is to say, it puts all its effort in the “many trivials”.
Some examples of such vital minorities would be:
- The minority of returns that represents the majority of customer complaints The minority of buyers that represent the majority of sales The minority of products, processes, or quality characteristics that cause the bulk of waste or reprocessing costs. The minority of sellers that are linked to the majority of contested parties. The minority of problems causing the bulk of the delay of a process. The minority of products or services that represent the majority of the profits obtained. The minority of elements that represent the bulk. of the cost of an inventory.
Its use is recommended:
- To identify opportunities for improvement To identify a product or service for analysis to improve quality When there is a need to draw attention to problems or causes in a systematic way To analyze different groupings of data When looking for the main causes of the problems and prioritize the solutions. To evaluate the results of the changes made to a process (before and after). When the data can be classified into categories. When the rank of each category is important.
When it's used?
- When identifying a product or service for analysis, to improve quality. When there is a need to draw attention to problems or causes in a systematic way. When identifying opportunities for improvement. When analyzing different groupings of data (eg, by product, by segment, market, geographic area, etc.) When looking for the main causes of problems and prioritizing solutions, When evaluating the results of changes made to a process (before and after) When the data can be classified into categories.When the rank of each category is important
How is it used?
- Select logical categories for the identified topic of analysis (include time period). Collect data. Using a Check List can be very helpful in this step. Sort the data from the highest category to the lowest. Total the data for all categories. Calculate the percentage of the total that each category represents. Plot the horizontal axes (x) and vertical (and primary - andPlot the scale of the left vertical axis for frequency (from 0 to total, as previously calculated), from left to right trace the bars for each category in descending order. If there is an “other” category, it should be placed at the end, regardless of its value. That is, it should not be taken into account when ordering the frequency of the categories from highest to lowest. Plot the scale of the right vertical axis for the cumulative percentage, starting from 0 and up to 100%. Plot the line graph for the cumulative percentage, starting at the top of the bar in the first category (highest) Give a title to the graph, add the dates when the data was collected, and cite the source of the data. Analyze the graph to determine the " few vitals ”
Application example
A refrigerator manufacturer wants to analyze which are the most frequent defects that appear in the units when leaving the production line. For this, he began by classifying all possible defects into their various types:
| Type of deffect | Problem Detail |
| Motor does not stop | Does not stop the engine when it reaches temperature |
| Does not cool | The engine starts but the refrigerator does not cool |
| Poor Weatherstripping | Broken or misshapen weatherstrip that does not fit |
| Poor Painting | Paint defects on external surfaces |
| Stripes | Scratches on external surfaces |
| It does not work | Plugging in won't start the engine |
| Door does not close | The door does not close properly |
| Poor bins | Interior cracks with cracks |
| Engine won't start | Engine does not start after stop cycle |
| Poor Leveling | Refrigerator sways and cannot be leveled |
| Door Def. | Refrigerator door does not close tightly |
| Others | Other Defects not included in the above |
Subsequently, an inspector reviews each refrigerator as it leaves production, recording its defects according to these types. After inspecting 88 refrigerators, a table like this was obtained:
| Type of deffect | Problem Detail | Freq. |
| Weatherstripping Defect | Broken or misshapen weatherstrip that does not fit | 9 |
| Default Paint | Paint defects on external surfaces | 5 |
| Defect drawers. | Interior cracks with cracks | one |
| Poor Leveling | Refrigerator sways and cannot be leveled | one |
| Engine won't start | Engine does not start after stop cycle | one |
| Motor does not stop | Does not stop the motor when it reaches temperature | 36 |
| Does not cool | The engine starts but the refrigerator does not cool | 27 |
| It does not work | Plugging in won't start the engine | two |
| Others | Other Defects not included in the above | 0 |
| Default Door | Refrigerator door does not close tightly | 0 |
| Door does not close | The door does not close properly | two |
| Stripes | Scratches on external surfaces | 4 |
| Total: | 88 |
The last column shows the number of refrigerators that presented each type of defect, that is, the frequency with which each defect occurs. Instead of the numerical frequency we can use the percentage frequency, that is, the percentage of refrigerators in each type of defect:
| Type of deffect | Problem Detail | Freq. | % |
| Weatherstripping Defect | Broken or misshapen weatherstrip that does not fit | 9 | 10.2 |
| Default Paint | Paint defects on external surfaces | 5 | 5.7 |
| Default Drawers | Interior cracks with cracks | one | 1.1 |
| Poor Leveling | Refrigerator sways and cannot be leveled | one | 1.1 |
| Engine won't start | Engine does not start after stop cycle | one | 1.1 |
| Motor does not stop | Does not stop the motor when it reaches temperature | 36 | 40.9 |
| Does not cool | The engine starts but the refrigerator does not cool | 27 | 30.7 |
| It does not work | Plugging in won't start the engine | two | 2.3 |
| Others | Other Defects not included in the above | 0 | 0.0 |
| Door Def. | Refrigerator door does not close tightly | 0 | 0.0 |
| Door does not close | The door does not close properly | two | 2.3 |
| Stripes | Scratches on external surfaces | 4 | 4.5 |
| Total: | 88 | 100 |
Now you can represent the data in a histogram:
Now, what are the defects that appear most frequently? To make it more evident, before graphing, the data in the table can be ordered in decreasing order of frequency:
| Type of deffect | Problem Detail | Freq. | % |
| Motor does not stop | Does not stop the motor when it reaches temperature | 36 | 40.9 |
| Does not cool | The engine starts but the refrigerator does not cool | 27 | 30.7 |
| Poor Weatherstripping | Broken or misshapen weatherstrip that does not fit | 9 | 10.2 |
| Def paint. | Paint defects on external surfaces | 5 | 5.7 |
| Stripes | Scratches on external surfaces | 4 | 4.5 |
| It does not work | Plugging in won't start the engine | two | 2.3 |
| Door does not close | The door does not close properly | two | 2.3 |
| Drawers Def. | Interior cracks with cracks | one | 1.1 |
| Poor Leveling | Refrigerator sways and cannot be leveled | one | 1.1 |
| Engine won't start | Engine does not start after stop cycle | one | 1.1 |
| Door Def. | Refrigerator door does not close tightly | 0 | 0.0 |
| Others | Other Defects not included in the above | 0 | 0.0 |
| Total: | 88 | 100 |
It can be seen that the category "others" should always go to the end, regardless of its value. This way, if it had had a higher value, it should still have been in the last row.
It is now clear what the most common types of defects are. It can be seen that the first 3 types of defects appear in approximately 82% of refrigerators. By the Pareto Principle, we conclude that: Most of the defects found in the lot belong to only 3 types of defects, so that if the causes that cause them are eliminated, most of the defects would disappear.
FLOWCHART
The Flow Diagram or Flowchart, consists of graphically expressing the different operations that make up a procedure or part of it, establishing its chronological sequence. Depending on its format or purpose, it may contain additional information on the method of execution of the operations, the itinerary of the people, the forms, the distance traveled, the time spent, etc.
Its importance is that it helps to designate any graphic representation of a procedure or part of it. The flowchart of knowledge or flowchart, as its name implies, represents the information flow of a procedure.
Currently flow charts are considered in most companies or systems departments as one of the main instruments in the realization of methods and systems, since they allow the visualization of unnecessary activities and verifies if the distribution of work is balanced, that is, well distributed in people, without surcharge for some while others work very comfortably.
Likewise, the flow chart helps the analyst to understand the information system in accordance with the operations of the procedures included, it will help him to analyze these stages, in order to improve them as well as to increase the existence of information systems for the administration..
Characteristics that Flowcharts must possess :
- Synthetic: The representation that is made of a system or a process should be summarized in a few sheets, preferably in one. Extensive diagrams make it difficult to understand and assimilate, so they are no longer practical. Symbolized: Applying appropriate symbology to system and procedure diagrams saves analysts from excessive, repetitive, and confusing notations in their interpretation. Visibly to a system or process: Diagrams allow us to observe all the steps of a system or process without having to read extensive notes. A diagram is comparable, in a way, with an aerial photograph that contains the main features of a region, and which in turn allows to observe these main features or details.
Symbology of elaboration of flow diagrams of general use
Document: any document (checks, purchase or sales invoices, etc.)
Manual process: any manual operation, such as preparing a sales invoice or reconciling a financial statement.
Process: any operation, either manually, mechanically or by computer. Often used also with the manual process symbol.
Offline storage: a file or other storage aid for documents or computer records.
Flow Lines: lines that indicate a directional flow of documents. Usually down or to the right, unless the arrows indicate otherwise.
Annotation - used to make explanatory comments, such as a file stream (by date, in alphabetical order, etc.)
Connector: output to, or input from, another part of the flowchart. It is used to avoid excessive crossing of flow lines. The input and output connectors contain letter or number keys.
Connector between different pages: indicates the source or destination of lines entering or leaving the flowchart.
In / Out: used to locate a connector from another page, to indicate information that enters or leaves the flow diagram.
Decision: Indicates alternate courses of action as a result of a yes or no decision.
Design and Elaboration of Flowcharts
This is governed by a series of symbols, standards and conventional guidelines which are:
- The format or skeleton of the flowchart must be divided into parts that represent the departments, sections or dependencies involved in the procedure. Each department or section must be shown only once in the flowchart and in the same order or chronological sequence of its appearance in the procedure described from left to right. The same unit must be shown more than once in the flowchart, even when Actions of the procedure return to it. The flow chart indicator lines must be thinner than the format dividing lines, straight and angular, with arrows at their terminal ends. Each step or action of the procedure must be clearly enumerated and briefly described with very few words.When any document is retained in any dependency of the flowchart, it is indicated according to whether it is archived: definitively, temporarily or retained for a few days (“D”), hours (“O”) or minutes (´) When a document must be destroyed after being used in the procedure is indicated with a large (X).When in the procedure some document gives rise to another it will be indicated in the flowchart by an interrupted arrow. Just as we saw in the flow charts in the flowcharts when several lines intersect without having relationship is indicated by an inflection in any of them. It will always be better if the flowchart is shown in a single sheet, but when in its extension it has to continue on another page, it is indicated by any symbol within a circle,on the page where it is interrupted and the same one that is usually called connector will be placed on another page as follows.
To complement we suggest the following 3 video-lessons in which the bases of cause-effect diagrams (Ishikawa), Pareto diagrams, and flow charts or flow charts are explained (28 minutes).
Download the original file
