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Online Student Guide

OpusWorks 2019, All Rights Reserved

Cause and Effect Diagrams

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Table of Contents

LEARNING OBJECTIVES ....................................................................................................................................4

INTRODUCTION ..................................................................................................................................................4 WHAT IS A “ROOT CAUSE”? ......................................................................................................................................................... 4 WHAT IS A “ROOT CAUSE ANALYSIS”?...................................................................................................................................... 4 ADDRESSING THE ROOT CAUSE .................................................................................................................................................. 5 ROOT CAUSE ANALYSIS: THREE BASIC STEPS ........................................................................................................................ 5 CAUSE AND EFFECT TOOLS .......................................................................................................................................................... 6

FIVE WHYS ...........................................................................................................................................................6 THE FIVE WHYS ............................................................................................................................................................................. 6 THE 5 WHYS: KEY BENEFITS ...................................................................................................................................................... 6 FIVE WHYS EXAMPLE ................................................................................................................................................................... 7 EVERYDAY LIFE SCENARIO .......................................................................................................................................................... 7 HOSPITAL SCENARIO ..................................................................................................................................................................... 8 ANOTHER WAY TO LOOK AT THE PROCESS ............................................................................................................................. 8

ROOT CAUSE ANALYSIS ....................................................................................................................................8 THINGS TO KEEP IN MIND DURING A ROOT CAUSE ANALYSIS ............................................................................................ 8 THE RESULT OF IMPLEMENTING A POORLY DESIGNED PROBLEM ..................................................................................... 9 DEFINING AND DETERMINING THE ROOT CAUSE ................................................................................................................... 9 FIRE FIGHTER VS. FACTS AND DATA DRIVEN ANALYSIS... ................................................................................................ 10 DEVELOPING THE PROBLEM SOLUTION ................................................................................................................................. 10 EXAMPLES OF FINDING THE SOLUTION ................................................................................................................................. 11

RULES OF CAUSE AND EFFECT .................................................................................................................... 11 THE RULES OF CAUSE AND EFFECT ........................................................................................................................................ 11 UNDERSTANDING WHAT WE CAN AND CANNOT CONTROL ............................................................................................. 12 RULE #1: EVERYTHING HAPPENS FOR A REASON .............................................................................................................. 12 RULE #2: CAUSE AND EFFECT ARE PART OF A CONTINUOUS CHAIN ............................................................................... 13 RULE # 3: AN EFFECT CAN RESULT IN BOTH A DIRECT CAUSE AND A CONDITIONAL CAUSE ................................... 14 ROOT CAUSE ANALYSIS DIAGRAM .......................................................................................................................................... 15 THE OVERALL PROCESS SUMMARY ........................................................................................................................................ 15

CAUSE AND EFFECT TOOLS .......................................................................................................................... 16 SOME TOOLS OF ROOT CAUSE ANALYSIS .............................................................................................................................. 16 CAUSE AND EFFECT TOOLS 2 ................................................................................................................................................... 16 GETTING IDEAS – BRAINSTORMING ........................................................................................................................................ 16

AFFINITY DIAGRAM ....................................................................................................................................... 16

THE FISHBONE DIAGRAM ............................................................................................................................. 17 FISHBONE DIAGRAM ................................................................................................................................................................... 17 CONSTRUCTING THE FISHBONE DIAGRAM ............................................................................................................................ 18 IDENTIFYING DIRECT AND CONDITIONAL CAUSES .............................................................................................................. 18 WHEN TO USE THE FISHBONE DIAGRAM ............................................................................................................................... 19

PARETO CHART ............................................................................................................................................... 19

XY MATRIX ........................................................................................................................................................ 20

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THE XY MATRIX .......................................................................................................................................................................... 20 DEFINING THE XY MATRIX ....................................................................................................................................................... 20 STEPS 1&2 HOW TO CONSTRUCT AN XY MATRIX .............................................................................................................. 21 STEP 3 HOW TO CONSTRUCT AN XY MATRIX ...................................................................................................................... 21 STEP 4 HOW TO CONSTRUCT AN XY MATRIX ...................................................................................................................... 21 STEP 5 HOW TO CONSTRUCT AN XY MATRIX ...................................................................................................................... 22 STEP 6 HOW TO CONSTRUCT AN XY MATRIX ...................................................................................................................... 22 STEP 7 HOW TO CONSTRUCT AN XY MATRIX ...................................................................................................................... 22 STEP 8 HOW TO CONSTRUCT AN XY MATRIX ...................................................................................................................... 23 CREATE A PARETO CHART FROM THE C&E MATRIX .......................................................................................................... 23

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Learning Objectives

Upon completion of this course, student will be able to: • Learn the three basic steps for identifying and preventing problems • Apply basic cause and effect principles in order to identify the root cause of a problem • Use techniques for gathering information for cause and effect analysis, including Five Whys and

Brainstorming • Organize data and information for analysis using the Affinity Diagram and the Fishbone (Ishikawa)

Diagram • Analyze a process using Root Cause Analysis and The XY Matrix

Introduction

What is cause and effect? Cause and effect means that an action or event will produce a reaction or response in the form of another event.

What is a “Root Cause”?

To learn about Cause and Effect Analysis, it is important that you understand the definition of “root cause.” Root cause is the fundamental breakdown or failure of a process or product, which when resolved and corrected, prevents recurrence of that failure or problem. Root cause analysis is an important technique which serves as the basis for several of the cause and effect tools we will learn about in this module. Root Cause Analysis is not limited to manufacturing processes or products. It is equally appropriate for administrative and service environments, such as healthcare organizations, offices, and financial institutions. This diagram shows that garden plants are dying, and it lists four causes. Can you tell which is the root cause? Here, the root cause of the problem is not apparent and to find it, we need to do a basic “Root Cause Analysis.”

What is a “Root Cause Analysis”?

Root Cause Analysis is a basic process improvement method. It is used to define and address a problem, non-conformance, or failure of a product or process in order to identify its root cause. Root Cause Analysis provides you with a structured methodology for defining, and then correcting or eliminating, the root cause of a problem in order to prevent its recurrence.

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It is a very effective tool teams can use to define the correct problem to address during problem solving and continuous improvement activities. Root Cause Analysis is typically used early in a process improvement project, usually in the Measure and Analyze phases of the DMAIC process.

Addressing the Root Cause

When a problem occurs in a process or product, a common first reaction is to address the symptom, rather than define the actual root cause. Let’s look at an example. In this diagram, the symptom is weeds in our yard. Since we can see the top of the weed plants, a typical reaction is to just pull them out. However, because this often leaves some roots behind, the weed grows back. As you see, we did not address the root

cause, which would have fixed the problem so the weeds would not grow back. Remember, Root Cause Analysis provides a method for defining and fixing the real problem.

A symptom is usually very obvious because it can often be seen above the surface, like our weed. However, because focusing only on the symptom does not typically fix the actual problem, the problem will likely reoccur.

Root Cause Analysis: Three Basic Steps

Now that you have a basic understanding of Cause and Effect and root cause and Root Cause Analysis, let’s take a look at the basic steps. Prior to beginning the Root Cause Analysis process, it is necessary to establish a team of process owners. All team members should be Subject Matter Experts (SMEs), with in-depth knowledge of the product and the process. Once the team is established, it follows three basic steps. The first step is to define the problem in terms of the effect or symptom that is observed. The second step is to analyze the process to determine why and when the problem happened. The third step is to develop a permanent solution to prevent the problem from reoccurring. We will examine the details of the Root Cause Analysis process later in this module. But first, we need to introduce some important tools and techniques.

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Cause and Effect Tools

Cause and Effect tools can be divided into three categories, according to the purpose. The first set of tools is for gathering ideas and includes Five Whys and brainstorming. Five Whys and brainstorming. Tools for organizing data and information include the Affinity Diagram and the Fishbone, or Ishikawa) Diagram. Some very powerful tools for analyzing cause and effect are the Root Cause Analysis, also known as the Current Reality Tree, and the XY Matrix. We will look at each of these tools, beginning with the Five Whys.

Five Whys

The Five Whys

The Five Whys is a simple problem solving technique used to quickly get to the root of a problem. It serves as the basis for many Root Cause Analysis methods. The 5 Whys was made popular in the 1970s by the Toyota Production System. The strategy involves looking at any problem and asking the questions, "Why?" and "What caused this problem?", over and over, until the root cause can be

determined. Although this simple technique is referred to as the Five Whys, the two questions may be asked as many times as necessary, depending on the complexity of the problem. Very often, the answer to the first "Why?" will prompt another "Why?"; the answer to the second "Why?" will then prompt another "Why?", and so on. Hence, the name: the Five Whys strategy.

The 5 Whys: Key Benefits

Some key benefits of the Five Whys include the following: It helps teams quickly determine the root cause of a problem. It is a structured approach to solve problems as they occur. It serves as a framework for a team to work through a more complex problem. It is simple, and easy to learn and apply.

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Five Whys Example

Because the Five Whys strategy is such a valuable and efficient tool for defining the real root cause of a problem, most Process Improvement practitioners learn to use it early in their skills development. Let’s look at a few examples of how it can be applied. Here is an example of how a team might use the Five Whys strategy in a production situation. First, the team defines the problem as the “wrong part received from the stockroom.” Next, the team asks “Why” this problem

occurred, and it determines that the part in stock was labeled with the wrong part number. This prompts the team to ask “Why” the part in stock was labeled with the wrong part number. It determines that the part was labeled wrong at the supplier. The team continues with this process, asking “Why?” three more times, and comes up with the three subsequent causes you see here. At this point, the team must determine whether it has asked “Why” enough times to reach the root cause, or if it can go deeper into the analysis. In this scenario, the team may need to continue its analysis to determine why the drawings awaiting a change order approval caused a problem with a supplier.

Everyday Life Scenario

Now let’s see how the Five Whys strategy might be used to analyze a simple problem of everyday life. In this example, imagine that you were late to work and missed an important meeting. You ask yourself “Why?” and realize that you overslept. When you ask yourself "Why" you overslept and you realize your alarm didn't go off, you ask yourself "Why" your alarm didn’t go off and determine that the alarm was set to 6pm rather than 6am. Digging deeper into your analysis, you ask “Why” yet again. At this point, you determine that the indicator light on your alarm clock, telling you if the time is set for am or pm, is defective. In this scenario, because the problem was not very complex, asking “Why?” just four times was sufficient to reach the root cause.

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Hospital Scenario

Let’s look at one more example of how to use the Five Whys of Root Cause Analysis. Here, our scenario is a problem in a hospital. In this example, the team begins by defining the problem as “delays in hospital patient medication turnaround time.” Next, the team of SMEs analyzes why the problem happened by asking “Why?” five times, as follows:

1. Why? The nurses have to wait for medication deliveries to the unit work area. 2. Why? Preparation of the first I.V. dosage takes too long. 3. Why? Too much time is wasted in the medication preparation area. 4. Why? Excessive walking is required between prep area work stations. 5. Why? The work area layout is inefficient. At this point, the team is satisfied that the inefficient work area layout is the real root cause of the problem.

Another Way to Look at the Process

The ability to identify the true root cause of a problem allows organizations to put appropriate corrective actions in place to prevent recurrence. When solving complex problems, it is often necessary for the team to think out of the box, and to ask “Why?” more than five times. In such cases, a Cause and Effect tree diagram is a very powerful technique teams can use, in conjunction with the Five Whys, to determine the real root cause.

Root Cause Analysis

Things to Keep in Mind During a Root Cause Analysis

To begin our detailed examination of Root Cause Analysis, let’s go over some important things to keep in mind during the process. When analyzing a problem to find the root cause, it is important to focus only on real issues, which include data driven facts, rather than thoughts, ideas, or the unsupported opinions of individuals or groups. The team must not let the problem’s symptom distract it from finding the real root cause. Remember, the visible part of a weed really is not the true root cause. The real cause is the root below the surface.

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Another important thing to remember during Root Cause Analysis is the saying, “Junk in delivers junk out.” In other words, if a team does a poor job defining and identifying the root cause, its organization could waste valuable resources chasing just a symptom.

Throughout Process Improvement methodology, facts and data are always a key focus. We refer to a symptom-driven problem solving as “Fire Fighting.” When a Fire Fighter approach is used for problem resolution, it typically results in poorly designed problem fixes.

The Result of Implementing a Poorly Designed Problem

The Titanic disaster is a real life example that clearly demonstrates why it is so important to avoid implementing a poorly designed problem fix. Let’s examine what happened. When the Titanic was built, the shipbuilder advertized it as “Unsinkable.” During the same time she was under construction, the shipbuilding industry placed a high demand on high quality steel rivets, causing a severe shortage. The shipbuilder, thinking of ways to resolve this issue, came to a poorly designed solution to the problem: Substitute iron rivets in place of the steel rivets. The iron rivets were substandard for marine applications, and not typically used for ships this size. As a quick fix to the problem, iron rivets were used in the bow and stern sections so the high quality steel rivets could be used in the main hull section. Ship design experts today, speculate that the substandard iron rivets broke prematurely during the ship’s initial impact, causing the ship to sink significantly faster that it would have if the higher quality rivets were used. History tells the rest of the tragedy. In problem solving, it is critical to focus on data driven facts and to make sure all aspects of the problem resolution, or fix, are the best for addressing the root cause. In the case of the Titanic, perhaps the shipbuilder should have addressed the real cause for the steel rivet shortage instead of implementing a poorly designed, substandard fix.

Defining and Determining the Root Cause

As you may expect, there is a very significant difference between the way Root Cause Analysis and Fire Fighter approaches define and resolve problems. Let’s do a side-by-side comparison of these two approaches. When a Fire Fighter approach is used, the problem is defined based on individual memory, perception, opinion, and the description of the

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problem symptom. Here, the cause is defined in relation to the symptom. With Root Cause Analysis, on the other hand, the problem is analyzed and defined by a team of SMEs, based on real-time information, accurate facts, and data. The symptom is viewed as evidence of the real root cause of the problem. Here, the cause is defined in relation to the true, defined problem.

Fire Fighter vs. Facts and Data Driven Analysis...

Another big difference between the Fire Fighter approach and Root Cause Analysis is the focus of the analysis. When an organization allows its team to become fire fighters that simply address the symptom, it typically defines the workforce as the source of the problem. The common perception is that if workers are trained and motivated to be more careful, the problem will fix itself. Here, there is never enough time or resources to truly define, and permanently fix, the root cause. Alternately, the Root Cause Analysis approach is based on the concept that mistakes and defects result from system generated faults. Here, people play only a small part. With this approach, mistake and error proofing are typically well designed and implemented. Organizations that use Root Cause Analysis understand that solving the real problem permanently is critical to their success. They take the time to fix the problem so it does not reoccur.

Developing the Problem Solution

As you learned earlier, the final step of problem solving is to develop the fix, or problem solution. By now, it should be very evident which of these two approaches is more effective for solving a problem. Let’s compare the results.

With the Fire Fighter approach, the team implements a quick fix for the very first cause it identifies. The team is not provided with the support it needs to define and develop the correct fix. Because the quick fix approach only hides the real cause under the symptom, rather than addressing the root cause of the problem, the error or defect typically returns. Now let’s review the results of the Root Cause Analysis approach.

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Here, a permanent, well designed solution is applied to the real cause, not a symptom. Leadership supports the problem solving team by providing the necessary time and resources. The team effectively “drills down” to the root cause by repeatedly asking the “Why?” question until the question can no longer be answered. When a well designed solution is implemented and mistake and error proofing is incorporated, the problem does not reoccur. Next, let’s take a brief look at an example.

Examples of Finding the Solution

Here you see an example of the Fire Fighter approach and the Root Cause Analysis approach being used to analyze the same problem. Take a moment to review how each approach was used to develop the solution. As expected, the solution results are very different.

Rules of Cause and Effect

The Rules of Cause and Effect

Next, we will examine the Root Cause Analysis process in detail to see how it is used to get to the heart of a problem. During a typical Root Cause Analysis, a chain of events occurs. This chain of events is defined by the principles of Cause and Effect. There are three basic rules of Cause and Effect, as follows: 1) Everything happens for a reason; 2) Cause and effect are part of a continuous chain; and 3) An effect can be due to both a cause and a condition. The principle of Cause and Effect is a key element of Lean thinking.

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Understanding What We Can and Cannot Control

In order to use Root Cause Analysis effectively, it is important to understand the concept of span of control and sphere of influence. This concept helps establish context so that root cause problem solving tools can be used more effectively. It also helps teams determine how deep to take their analysis. Put simply, the concept of span of control and sphere of influence helps teams determine when they have reached the root cause. The concept is based on the fact that we all function in complex systems, and we have some degree of control over our environment.

In relation to problem solving, areas where a team has a high degree of control, or full authority to get things done, fall within the span of control. Likewise, the areas where it does not have direct control, but can exert an influence, fall within the sphere of influence. Beyond these first two regions, there is an area where the team does not have any control or influence. This is called the outside environment. The concept of span of control and sphere of influence is important for Root Cause Analysis and effective problem solving because it enables the team to understand what it can, or cannot, accomplish in order to fix the root cause of its problem. For example, think back to our Five Whys hospital illustration. As you recall, the hospital was experiencing delays in patient medication turnaround time, and the team determined the root cause to be an inefficient work area layout. If a major capital investment were required to correct the inefficient work area layout, it would most likely be an outside environment issue. In this case, the team might need to consider a less costly area rearrangement, within the budget constraints of the local department manager. Keep in mind, the root cause is the lowest point in the Cause and Effect chain that the team can affect within its span of control and sphere of influence.

Rule #1: Everything Happens for a Reason

Now let’s return to the three basic rules of Cause and Effect. The first rule of Cause and Effect states that everything happens for a reason. When we consider the age-old question of why the apple falls from the tree, we automatically think about Newton’s Law of Gravity.

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The apple falls because of the effect of Earth’s gravity. This basic rule can be applied to just about everything that happens, from why a person tripped over an extension cord to why your car ran out of gas. There is always a reason why something happens.

Rule #2: Cause and Effect are part of a continuous chain

The first rule of Cause and Effect, that everything happens for a reason, leads into the second rule, which states that Cause and Effect are part of continuous chain. As a team begins its process of “drilling down” to determine the true root cause of its problem, it should look at the problem as being caused by

a series, or chain, of events, each of which happens for a reason. This chain of causes can be continuous, and go on and on, as long as the team continues to ask “Why?”

In problem solving, the point at which the team begins asking “Why?” is based on where it first sees the effect or symptom. It begins at the point of an effect it can observe and wishes to correct. In this diagram, that point is “Wrong part received from stockroom.” The team stops asking “Why?” when it can honestly admit it doesn’t know the answer. This stopping point can occur after it has asked “Why?” just one or two times, or many times. At the end of this chain of causes, is the root cause. Recall that the root cause solution, and action required to prevent reoccurrence, must be within the team’s control or influence. To illustrate, let’s go back to our production example, where the wrong part was received from the stock room. In this illustration, although “Drawings awaiting change order approval” is at the end of the chain, it may not be a root cause the team can correct at this point. For example, although leadership may be

aware of the backlog of approvals, it may have decided to live with the delays until it selects a new person to approve changes. One option for the team, in this case, could be to make leadership aware of the problem and how it is affecting the organization. The team could also be proactive, and suggest a temporary approval process or person.

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Rule # 3: An Effect can result in both a Direct Cause and a Conditional Cause

The third rule of Cause and Effect states that an effect can result in both a direct cause and a conditional cause. Let’s take a look at what this means. Confronted with an effect, the team begins to investigate by following the “Why?” to the direct cause. As demonstrated in Rule #2, the team may continue to ask the “Why?”, but there is a better technique. At this point the team can test the existing cause-effect relationship by stating, “If cause, then effect.”

When the direct cause does not immediately result in the effect, and needs some help, it may signal the presence of a conditional cause. The team may find that the effect could have two or more causes. This rule is often overlooked, or not included, in Root Cause Analysis cause-effect methods. This is a mistake, however, because drilling down on both the direct causes and the conditional causes can lead to some very interesting, and often surprising, results. In fact,

many of the most creative solutions come from investigating the conditions. This is a very powerful technique, which takes some thought and practice to master. Next, let’s look at an example. Let’s go back, once again, to our production example, in which the wrong part was being received from the stockroom. Recall that parts in stock were labeled with the wrong part number. The team asked “Why?” and determined that they were labeled wrong at the supplier. Now, it considers the statement, “IF the parts are labeled wrong at the supplier, THEN the parts in stock will be labeled incorrectly.” With this statement in mind, the team then asks, “Will this cause always result in the effect, or does it need a contributing factor, or conditional factor, to make it true all of the time?” Let’s see if the cause in our example will always result in the effect, or if it needs a contributing factor to make it true all of the time. As you see here, parts labeled wrong at the supplier will result in the wrong parts in stock only if there is no incoming inspection or verification. Therefore, this is a conditional cause.

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To illustrate this on the chart, it is linked to the direct cause with an “and” symbol, or ellipse. Now the team can state, “If the parts are labeled wrong at the supplier AND there is no incoming inspection or verification, then the parts in stock will be labeled with the wrong part number.” Notice that the team can ask “Why?” for both the direct cause and the conditional cause. This is a very powerful technique, which will open new possibilities for investigation. In this scenario, for example, the team can now ask, “Why is there no

incoming inspection or verification?”

Root Cause Analysis Diagram

Here is an example of a detailed Cause and Effect diagram for a cafeteria grill grease fire. This is also known as the Current Reality Tree for a specific problem or effect.

The Overall Process Summary

As you learned earlier, when a team begins the process of “drilling down” to determine the true root cause of a problem, it should think of the problem as being caused by a chain of events. This is why the Five Whys approach is so effective in defining the root cause. Before we move on to introduce some tools for Root Cause Analysis, let’s summarize the overall process. The first step of Root Cause Analysis is to define the problem, failure event, or undesirable effect (UDE). In other words, “What is the problem?” The second overall step of Root Cause Analysis is to analyze the problem. The team starts by looking under the problem to understand the causes of the failure. To do this, it works backwards to identify the direct cause. Remember, direct cause is typically not the root cause. Once it has identified the direct cause, the team seeks out any contributing causes, using the Five Whys strategy. It then continues to drill down the chain until arriving at the root cause.

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The root cause is the fundamental problem, or the lowest point of the cause and effect chain that is within the team’s control or influence.

Cause and Effect Tools

Some Tools of Root Cause Analysis

There is a vast array of tools that can be used during Root Cause Analysis. In this module, we will highlight several of these tools, with our primary focus on the Fishbone diagram and the XY matrix.

Cause and Effect Tools 2

Earlier in this module, you learned how the Five Whys can be structured into a Root Cause Analysis, also called a Current Reality Tree. Now we will look at several other tools for gathering, analyzing, and organizing ideas in order to troubleshoot a process. Keep in mind that although many of these tools have a variety of uses, we will examine them solely from the cause-effect perspective.

Getting Ideas – Brainstorming

The objective of a brainstorming session is to quickly generate as many ideas as possible. Once the team defines the problem, the next step is to ask people to give their ideas. It is important that everyone has a fair opportunity to participate. It often helps to include a facilitator for this activity, and to establish and post ground rules in the area.

Affinity Diagram

The next tool we will look at is the Affinity Diagram. An Affinity Diagram is a tool that gathers large amounts of language data (such as ideas, opinions, and issues), and organizes it into groupings based on natural relationships. Overall, it is a simplistic tool for organizing “language data”; focusing the team on a problem or

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topic; generating ideas through brainstorming, and organizing those ideas; and achieving consensus. It is best to use an Affinity Diagram in situations where the team is drowning in ideas, the problem is complex, or chaos exists. The example you see here shows that four people had inputs, as represented by the four colors. When individual team members write independently, the ideas typically stream. The team members can use “post-it” notes to write their ideas, or the team can assign someone to take notes. Afterwards, the team groups the ideas. It then identifies duplicates and condenses the ideas into new groups or categories.

The Fishbone Diagram

Fishbone Diagram

When a team approach is used for problem solving, it usually generates many ideas as to the problem’s root cause. The Cause and Effect diagram, commonly called a Fishbone, is one way to capture these different ideas, and to stimulate the team’s brainstorming on root causes. Yet another name for the Fishbone diagram is the Ishikawa diagram. It is the brainchild of Kaoru Ishikawa, who pioneered quality management processes in the Kawasaki shipyards. In the process, he became one of the

founding fathers of modern management. The Fishbone visually displays the many potential causes for a specific problem or effect, and immediately sorts ideas into useful categories. For this reason, it can be used to structure a brainstorming session. It is particularly useful in a group setting and for situations in which little quantitative data is available for analysis. Next, we will take a closer look at how the Fishbone is used and constructed.

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Constructing the Fishbone Diagram

First, you start by identifying the undesirable effect or problem. The effect is shown on the right side of the diagram. After identifying the effect, the major categories for possible causes are selected. Generally the causes can be divided into five or six major categories. The categories are the “major bones” of the fish. We will use these six generic categories; Process, People, Measurement, Environment, Equipment and Materials. You can use these categories or create categories of your own.

The next step is for the team to brainstorm for ideas or potential causes related to the effect. You can start by brainstorming a list of ideas and then placing these ideas within the cause headings.

Identifying Direct and Conditional Causes

This is an example of a fishbone diagram for Late Invoicing. The effect or problem is written in, then the major categories. Now each possible cause must find its place under a major category. A very common mistake in constructing the C&E diagram is to describe causes using vague words like “Lack of…”. Notice that one of the causes is described as “Lack of proper Documentation”. That’s not very specific or even clear where it should go. Lack of proper documentation referred to the shipping area not having a

defined procedure for combining customer orders. So a better way to write that might be, “No procedure exists for combining orders in shipping.” That is much clearer and more specific. The team should exhaust the possibility of leaving something out by following the root cause chain of events to its conclusion. When a reason is exposed along the way they should avoid the use of generalities by using specific terms to describe those reasons.

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When to use the Fishbone Diagram

The Fishbone diagram is typically constructed in a team environment. Problem solving or continuous improvement teams can use it to study a problem or issue to determine the root cause. It can also be used to examine the potential reasons why a process or product is having difficulties, problems, breakdowns, or failure. Two additional uses for the Fishbone are to identify areas for data and information facts collection, and to evaluate why a process is not performing properly or producing the desired results. The Fishbone is most useful as a brainstorming tool. It helps capture everyone's ideas and thoughts in a structured manner.

Pareto Chart

Another tool that can be used during Root Cause Analysis is the Pareto diagram. The Pareto diagram is a graphic overview of the types and frequency of product or process defects. It ranks problems from the most frequent, called the Vital Few, to the least frequent, or the Trivial Many, in descending order from left to right. Using a Pareto Chart during Root Cause Analysis

can help the team decide which fault or defect is the most serious, or most frequent, offender. The principle was developed by Vilfredo Pareto, an Italian economist and sociologist, who studied wealth and poverty in Europe during the early 1900s. The basic principle behind Pareto's law is that in almost every case, 80 percent of the total problems incurred are caused by 20 percent of the problem cause types. By concentrating on the major problems first, the majority of other problems can be eliminated. The problems that have the most frequent occurrence are most likely to contain the root cause.

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XY Matrix

The XY Matrix

The XY matrix, also called the Cause and Effect (or C and E) matrix, is another Root Cause Analysis and problem solving tool. It is used to determine which inputs, or potential causes, of the process have the greatest impact when compared to customer requirements that are critical to quality (or CTQs). Here, X represents the inputs, or potential causes, and the Y represents the the CTQs. This tool applies when there are several problems or effects, and several potential solutions that can impact several problems. Potential problem causes are prioritized by examining their relationship with the CTQ requirements. Throughout the remainder of this module, we will refer to this tool as the XY matrix. Remember, however, that it is also called the Cause and Effect (or C and E) matrix.

Defining the XY Matrix

By rating customer requirements for importance, and rating the relevance of each process step to each requirement, the XY matrix helps identify which aspects of the process are most important or significant. When constructing the XY matrix, the CTQs, or problem effects, are placed on the top, and the causes, or process steps, are placed along the left side. The CTQs are ranked in terms of importance. Likewise, the relationships between the causes and CTQs are also ranked. The overall scores are then calculated. The cause with the highest overall score should be addressed first because it has the biggest impact on the CTQs. This cause could also become the root cause of the problem or effect. Now that you have a top level understanding of how the XY matrix is constructed and utilized, let’s walk through the details of each step.

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Steps 1&2 How to Construct an XY Matrix

Step One for constructing an XY matrix is to clearly define the project or problem being addressed. In the example shown here, the project is to reduce the cycle time for completing engineering change orders (or ECOs). Most likely, this project resulted from a problem identified by customers. Stated as a problem or effect, it could say; “The completion cycle time for ECOs is too long and must be reduced.”

Step Two is to identify the customer requirements or problem effects, and list them across the top of the matrix. As you recall, these are also known as the Y variables or CTQs.

Step 3 How to Construct an XY Matrix

Step Three is to rate the CTQs on a scale of one to ten, based on their importance in relation to the problem or customer. On the rating scale, ten is the highest importance and one is the least. Record the ratings in the top row for each CTQ column.

Step 4 How to Construct an XY Matrix

Step Four is to list the problem causes or process steps (Xs) on the left side of the matrix, in order of occurrence from first to last.

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Step 5 How to Construct an XY Matrix

Step Five is to determine correlation scores between each cause and CTQ. These scores are based on the strength of their relationship. For example, a score of “one” means the relationship strength is weak; a

score of “three” means there is some relationship; and a score of “nine” means the relationship is strong. In this example, under the first column, Timely Notification, the team determined that there is a strong correlation with the first cause or process output, so it entered a score of nine. Likewise, the team determined that there is some correlation with Cause Two, and weak correlation with Cause Three. Therefore, it entered scores of three and one respectively. This process is repeated for each CTQ and process step or cause.

Step 6 How to Construct an XY Matrix

Step Six is to cross multiply correlation scores with priority scores, and then add across for each cause. Looking at the example here, you see that the team multiplied the first column’s CTQ ranking of ten by Cause One’s relationship strength ranking of nine. Ten times nine is 90. The team repeated this process for Columns Two, Three, and Four. It then added the four numbers together to arrive at a total effect weight of 243. This process is repeated for each potential cause or process step.

Step 7 How to Construct an XY Matrix

Step Seven is to sum the relationship strengths for each column to arrive at a total for each column. For example, in this matrix, the sum of the relationship strengths for Column One, Timely Notification, is 33. Repeat this step for the row Total column. In this example, the sum of the row Total column equals 1347.

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Step 8 How to Construct an XY Matrix

Step Eight is to calculate the percent contribution of each cause. To do this, divide each row Total (from the column on the right), by the overall sum Total of that column. Then multiply that number by 100 to arrive at a percent figure. Record the percentage for each cause in its corresponding row. In this illustration, for example, the team divides 243 (the row Total of Cause One) by 1347, to arrive at 0.1804. It then multiplies 0.1804 by 100 to arrive at a percentage figure of 18.04. The team records 18.04 percent in the first row of the percentage column. It then repeats this process to find the percent contribution for each row.

Create a Pareto Chart from the C&E Matrix

The final step for utilizing the XY matrix is to create a Pareto chart from the XY rankings. Because the Pareto Chart ranks problems from the most frequent to the least frequent, it helps determine on which cause, or process input, to focus improvement activity. Keep in mind that to obtain greater resolution, additional detailed process maps and XY metrics may be required.