Constructing the Basic House of Quality

7.4 Basic Matrix Structure

The QFD process is represented by a series of interconnecting matrices that establish the WHAT, the HOW's and the interrelationship of all parameters involved in the product development process. The QFD method is simply a disciplined way of deploying the voice of the customer (VOC) through each stage of the product cycle. The objective is to keep all efforts focused on the VOC requirements, to optimize cost and to minimize cycle time while being driven by the VOC.

The QT's are used in each product phase to communicate the knowledge developed to the next stage. In each stage translations take place to systematically bring the VOC to actions taken by functional organizations that result in a product/service that satisfies the customer. The purpose of the QT charts is to focus on answering three questions; WHAT, HOW and HOW MUCH. For each product stage and for each action taken in that stage these three questions must be addressed.

The “House of Quality”, sometimes referred to as the “Enhanced House of Quality” consists of multiple “rooms”.  Four of the “rooms” are lists that capture the, “What’s, How’s, Why’s and How Much’s” of the project.  Four additional “rooms” are formed by determining the correlation and relationships between these lists.  Figure 7-4 illustrates the basic structure and location of these “rooms”.  The following sections provide detail in forming the lists and relationships between these “rooms” that make up the “House of Quality”.  All four phases of the hierarchical matrices follow this basic structure and form.

Figure 7-4 The rooms and relationships of the house of quality.

7.4.1 Voice of the Customer (The “What’s”) - QFD starts with a list of objectives, or the WHATs that we want to accomplish. In the context of developing a new product this is a list of customer requirements and is often called the Voice of the Customer (VOC).  The items contained in this list are usually very general, vague and difficult to implement directly; they require further detailed definition. These vague needs are sometimes called “verbatims”, (e.g. easy to use, lasts long time, light weight, low power, easy to modify).

                       

Figure 7-5  The “what’s” defined by the VOC are often general statements.

One such item might be “easy to test”, which has a wide variety of meanings to different people. This is a highly desirable product feature, but is not directly actionable.

7.4.2 Transformation of Action - Once the list of WHAT’s is developed, each requires further definition. The list is refined into the next level of detail by listing one or more HOW's for each WHAT, (i.e. How are we going to satisfy the WHAT’s) as shown in Figure 7-6. This process can be further refined and expanded into a more detailed list of HOW’s.

                                   

Figure 7-6 The list of WHAT’s are transformed into a list of HOW’s

The objective of this refinement is to identify each actionable requirement - one that a clear action taken will satisfy a WHAT.

7.4.3 Handling Complex Relationships - The problem that is encountered is depicted in Figure 7-7. Many of the HOWs identified affect more than one WHAT. The approach to charting the `WHATs and `HOWs sequentially would become a maze of lines due to interrelationship that exist between the parameters

Figure 7-7 Many HOW’s affect more than one WHAT

7.4.4 Structuring the Relationships in a Matrix - The complexity of the sequential process is solved by creating a matrix with the HOW list across the top (horizontally) and the WHAT list vertical down the side of the matrix.  This determines the RELATIONSHIPS of the WHAT’s and HOW’s in a matrix where each intersect.  This is called a Correlation Matrix. Figure 7-8 illustrates by the use of a “X” where the What’s and How’s are interrelated.

Figure 7-8 A correlation matrix determines the relationships between the WHAT’s and HOW’s

7.4.5 Kinds of Relationships - The RELATIONSHIPS are the third key element of any QFD matrix and are depicted by placing symbols at the intersections of the WHATs and HOWs that are related. It is possible to depict the strength of the relationships by using different symbols. Commonly used symbols are shown in Figure 7-9.

Figure 7-9 Symbols used to show the strength of relationships.

This method allows very complex relationships to be depicted graphically and is easily interpreted as shown in Figure 7-10.

Figure 7-10 Strength symbols are placed in the matrix relating each WHAT to its respective HOW’s.

Throughout the QFD process there are repeatedly opportunities to cross check thinking, thus leading to better and more complete designs.  This technique of evolving plans into actions is useful for new product development as well as applications in business planning and systems design.

7.4.6 Target Values (How Much) - The fourth key element of any QFD chart is the HOW MUCH section. These are the measurements for the HOWs. These target values should represent what is necessary to satisfy the customer and may not be current performance levels.  Easy to test, when translated into detailed requirements may be measured in terms of the number of test points, requirement for component spacing, component edge clearance, etc. The component clearance would be a HOW and the HOW MUCH would be 0.020 inches minimum.  HOW MUCH's are needed for two reasons:

1.      To provide an objective means of assuring that requirements have been met.

2.      To provide targets for further detailed development

 Figure 7-11 The HOW MUCH’s are added in rows at the bottom of the matrix.

The HOW MUCH's, added to the matrix as shown in Figure 7-11, provide specific objectives that guide the subsequent design and afford a means of objectively assessing progress, minimizing ``opinion-eering ''.  The HOW MUCH's should be measurable as much as possible, because measurable items provide more opportunity for analysis and optimization than do non-measurable items.  This aspect provides another cross check on thinking. If most of the HOW MUCH's are not measurable then the definition of the HOW's are not detailed enough.  The HOW relationships that relate to the WHAT's become one means to check and measure to see if the WHAT requirements are being met. Viewed another way; meeting the target values will satisfy the HOW requirement.  If all of the HOW requirements are satisfied that are related to a VOC item by the relationship matrix then the VOC item is met. Therefore the focus can be now on meeting the target values and not be directly concerned with the VOC, it is taken care of by fulfillment of the HOW MUCH's.  These four key elements (WHAT, HOW, RELATIONSHIPS, HOW MUCH) form the foundation of QFD, and can be found on any QFD chart.

7.4.7 Correlation Matrix - The CORRELATION MATRIX is a triangular table often attached to the HOWs, establishing the correlation between each HOW item. The purpose of this roof-like structure is to identify areas where trade-off decisions, conflicts and research and development may be required. As in the RELATIONSHIP MATRIX, symbols are used to describe the strength of the relationships. The CORRELATION MATRIX also describes the type of relationship. The symbols commonly used are shown in Figure 7-12.

Figure 7-12 Symbols used to indicate correlation between pairs of HOW’s.

The correlation matrix identifies which of the HOWs support one another and which are in conflict.  Positive correlations are those in which one HOW supports another HOW. These are important because some resource efficiencies are gained by not duplicating efforts to attain same result. If an action adversely affects one HOW, it will have a degrading effect on the other. Negative correlations are those in which one HOW adversely affects the achievement of another how. These conflicts are extremely important; they represent conditions in which trade-offs are suggested. If there are no negative correlations there is probably an error. A well optimized product is almost always the result of some level of trade-off, which is expressed by a negative correlation.

Generally every HOW MUCH item has a desired direction. For example, POWER of 100 watts; generally driving it lower is better. A good test  for determining if a relationship is positive or negative is to ask the  question: "If power is driven towards its desired direction, are the other HOW's driven toward or away from their desired target values? If the HOW is driven towards its desired target value when power goes towards its desired target value then it is a POSITIVE RELATIONSHIP. If it is driven away from its desired target value then it is a NEGATIVE RELATIONSHIP."

Be cautious not to jump to a trade-off too quickly. The goal is to accomplish all of the HOW’s in order to satisfy customer requirements. The response to a negative correlation should be to seek a way to make the trade-off go away. This may require some degree of innovation or a research and development effort that may lead to a significant competitive advantage.

Figure 7-13 The correlation matrix is constructed on top of the HOW’s.

Frequently, negative correlations indicate conditions in which design and physics are in conflict. When this occurs physics always wins. Such trade-offs must be resolved. Trade-offs that are not identified and resolved often lead to unfulfilled requirements even though everyone has done their best. Some of the trade-offs may require high level decisions because they cross engineering group, department, divisional or company lines. Early resolution of these trade-offs is essential to shorten program timing and avoid nonproductive internal iterations while seeking a nonexistent solution.

Trade-off resolution is accomplished by adjusting the values of HOW MUCH's. These decisions are based on all the information normally available: business and engineering judgment as well as various analysis techniques. If trade-offs are to be made, they should be made in favor of the customer and not what is easiest for the company to perform.

7.4.8 Competitive Assessment - The COMPETITIVE ASSESSMENT is a pair of graphs that depict item for item how competitive products compare with current company products. This is done for the WHAT’s as well as the HOW’s. The COMPETITIVE ASSESSMENT of the WHAT’s is often called a Customer Competitive Assessment, and should utilize customer oriented information. It is extremely important to understand the customer's perception of a product relative to its competition.

The COMPETITIVE ASSESSMENT of the HOW’s is often called a Technical Competitive Assessment, and should utilize the best engineering talent to analyze competitive products. The COMPETITIVE ASSESSMENT can be useful in establishing the value of the objectives (HOW MUCH's) to be achieved.  This is done by selecting values which are competitive for each of the most important issues. The COMPETITIVE ASSESSMENT provides yet another way to cross check thinking and uncover gaps in engineering judgment. If the HOW’s are properly evolved from the WHAT’s, the COMPETITIVE ASSESSMENTs should be reasonably consistent.

WHAT and HOW items that are strongly related should also exhibit a relationship in the COMPETITIVE ASSESSMENT.  For example, if we believe superior dampening will result in an improved ride, the COMPETITIVE ASSESSMENT would be expected to show that products with superior dampening also have superior ride; as illustrated in Figure 7-14.

If this does not occur, it calls attention to the possibility that something significant may have been overlooked. If not acted upon, we may achieve superior performance to our “in house" tests and standards, but fail to achieve expected results in the hand of our customers.

The IMPORTANCE RATING is useful for prioritizing efforts and making trade-off decisions. Numerical tables or graphs will depict the relative importance of each WHAT or HOW to the desired end result. The WHAT IMPORTANCE RATING is established based on customer assessment. It is expressed as a relative scale (typically 1-5) with the higher numbers indicating greater importance to the customer. The importance ratings are listed in a column between the WHAT’s and the matrix. It is important that these values truly represent the customer, rather than internal company beliefs. Since we can only act from the HOW’s, importance ratings for these HOW’s are needed.

Figure 7-14 Competitive assessment of the WHAT’s are put in a box on the right side of the matrix.

7.4.9 Importance Ratings - Weights are assigned to the RELATIONSHIP symbols, e.g. the 9-3-1 weighting shown in Figure 7-15 achieves a good variance between important and less important items. Other weighting system may be used.  For each column (or HOW), the WHAT importance value is multiplied by the symbol weight, producing a value for each RELATIONSHIP. Summing these values vertically defines the HOW importance value. In Figure 7-16 the HOW importance rating for the first column is calculated in the following manner.  The double circle symbol weight (9) is multiplied by the WHAT importance value (5), forming a RELATIONSHIP value of 45. The next double circle symbol weight (9) is multiplied by the WHAT importance value (2), forming a RELATIONSHIP value of 18. These two values (45 + 18) form the HOW importance value of 63. This process is repeated for each column as shown in Figure 7-16.

 Figure 7-15 Importance ratings are obtained by assigning weights to the symbols in the relationship matrix

Figure 7-16 Importance ratings are calculated for each HOW as the sum of the weighted importance of each WHAT.

The IMPORTANCE RATING for the HOW’s provides a relative importance of each HOW in achieving the collective WHAT’s. We see that for the HOW’s listed; “Maximum Power” with a Target Value of 200 watts has the “HIGHEST” Relative Importance. Greater emphasis should be placed on the HOW with the 83 rating than the other HOW’s. It is important that we are not blindly driven by these numbers. The numbers are intended to help us, not constrain us. Look upon the numbers as further opportunities to cross check thinking. Question the relative values of the numbers in light of judgment. Is it reasonable that the HOW valued at 83 is the most important? Is it reasonable that the HOW’s with similar ratings are nearly equal in importance?

7.4.10 The Basic Matrix Structure - The previous section can now be integrated together into one chart. Figure 7-17 illustrates the Basic Matrix Structure. All of the matrices used in the product development stages could have these basic sections. Note the correlation matrix when added to the relationship matrix takes on the shape of a house with a roof. It is from this construction that the QFD matrices are termed the ̏houses of Quality''.

Figure 7-17 The basic form of the House of Quality relates the VOC and competitive assessment information to design requirements.