Welcome to an interactive tutorial on the House of Quality (HOQ) matrix. This matrix forms the central tool of Quality Function Deployment (QFD) and is its most recognized form. It is utilized by a multidisciplinary team to translate a set of customer requirements (the “Voice of Customer” – VOC), market research and technical benchmarking data into an appropriate number of prioritized engineering targets to be met by a new product design.
In this tutorial you are able to navigate the HOQ and learn about the completion of each section, based on the construction of the following matrix.
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QFD was first put forth in 1966 in Quality Assurance work done by Prof. Yoji Akao and Mr. Oshiumi of Bridgestone Tire. Its purpose was to show the connections between true quality, quality characteristics, and process characteristics. This was done using the Fishbone Diagram, with true quality in the heads and quality and process characteristics in the bones. For more complex products, Mitsubishi Heavy Industry Kobe Shipyards combined these many fishbones into a matrix. In 1979, Mr. Sawada of Toyota Auto Body used the matrix in a reliability study which permitted him to address technical trade-offs in the quality characteristics. This was done by adding a "roof" to the top of the matrix, which he then dubbed the "House of Quality."
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The House of Quality is actually an assembly of other deployment hierarchies and tables. These include the:
- Quality Characteristics Hierarchy/Customer Requirement (columns)
- The Quality Planning Table/Planning Matrix (right side room),
- Demanded Quality Hierarchy/Technical Requirement (rows)
- The relationships matrix which relates them using any one of several distribution methods/inter-relationship (central)
- Roof and,
- Design Planning/Target Table (bottom room).
Picture 1 - The House of Quality Structure
Or, detail the deployment of the Hose of Quality is shown bellow!
Picture 2 – The House of Quality to deploy Quality Function Deployment (QFD)
- Quality Characteristics Hierarchy/Customer Requirement (columns)
This is generally the first portion of the House of Quality (HOQ) matrix to be completed and also the most important. It documents a structured list of a product’s customer requirements described in their own words (the Voice of the Customer – VOC)
This information is usually gathered through conversations with the customer/survey in which they are encouraged to describe their needs and problems.
The list of requirements gathered in such an exercise must be structured before its entry into the HOQ. The construction of Affinity and Tree Diagrams can be used to do this.
To build an affinity diagram each customer statement is written onto a separated card. These cards are then arranged into groups with perceived associations by the QFD team.
Picture 3 – Gathering and Grouping the Customer Need
From each group a title card is chosen which encapsulates the meaning contained within that group. This can require the making of a new title card.
A second grouping exercise can be used to sort these group title cards to identify higher level associations. These groups can also be allocated titles which may again be sorted. The resulting group structure is illustrated in an Affinity Diagram.
Picture 4 – Affinity Diagram
The completed affinity diagram can then be used as the basis of a tree diagram. This is constructed from the top down with each level being considered in turn for errors and omissions. The result is a family tree type hierarchy of customer needs.
This structure is then documented in the customer requirement portion of the HOQ matrix.
Picture 5 – Deployment of Customer Requirement Matrix
- The Quality Planning Table/Planning Matrix (right side room)
The planning matrix attached to the right side of the House of Quality (HOQ) matrix, serves several purposes. Firstly it quantifies the customers’ requirement priorities and their perceptions of the performance of existing products. Secondly it allows these priorities to be adjusted based on the issues that concern the design team.
The measures used in this section are generally gathered from customers using a questionnaire.
The first and most important measure in this section is the requirement Importance Weighting. This figure quantifies the relative importance of each of the customer requirements (described in the left hand portion of the HOQ matrix) from the customer’s own perspective.
This measure is often shown in a column alongside the customer requirement description in the left section of the HOQ matrix.
A questionnaire is used to gather these importance weightings. In this a customer is asked to give an importance weighting for each documented requirement generally using a pre-defined scale.
A better but more involved approach is to use the Analytical Hierarchy Process (AHP). This also utilizes a questionnaire but offers the customer pairings of requirements to consider. They choose the most important from this pair. These results are then interpreted into numerical weightings using a matrix.
Picture 6 – Simple Determining Importance Weight
When combining questionnaire data gathered from a number of customers, care should be taken to ensure only a single market segment is considered in any one HOQ matrix. Generally the importance weighting entered into the matrix will be the average from the sample gathered. If this sample includes differing segments this mean figure will not be any value to the product design team. Using a Voice of the Customer Table is useful for identifying segments in an existing sample.
The second commonest component of the planning matrix provides a measure of the satisfaction of customer with available products. They are asked to consider the performance of each of the existing products in fulfilling their specified requirements. As for the importance weighting, a questionnaire can allow the selection of a value on a predefined scale or provide product pairs for consideration when AHP is utilized. This data is often illustrated graphically in the HOQ.
Picture 7 – Customer Satisfaction of Our and Competitor Products/Services
Other measures which are determined by the design team can also be included in the planning matrix. These can include:
- Planned satisfaction Rating
- Improvement Factor
- Sales Point
These measures are combined with the customer’s importance weightings to calculate an overall weighting for each customer requirement.
The Planned Satisfaction Rating quantifies the design team’s desired performance of the envisaged product in satisfying each requirement.
An Improvement Factor can then be calculated by subtracting the performance score of the company’s existing product from its planned performance score i.e. the number of improvement points. This difference is multiplied by an improvement increment (e.g. 0.2) and this is added to 1 to give the improvement factor.
A Sales Point measure can be used to add weight to those requirements which can be utilized to market the product (usually between 1 and 1.5).
Additional measures (e.g. environmental impact, competitor’s future action etc.) can also be included where these are deemed useful by the team.
An Overall Weighting relating to each requirement can then be calculated by multiplying the Importance Weighting by the Improvement Ratio and the Sales Point.
Picture 8 – Planning Matrix Deployment
- Demanded Quality Hierarchy/Technical Requirement (rows)
This section of the House of Quality (HOQ) matrix is also referred to as the engineering characteristics or the Voice of the Company. It describes the product in the terms of the company.
This information is generated by the QFD design team who identify all the measurable characteristics of the product which they perceive are related to meeting the specified customer requirements.
In the same way that customer requirements are analyzed and structured, affinity and tree diagrams are applied to interpret these product characteristics (see the customer requirement section of this tutorial for more details).
An additional row is often included in this section to illustrate the direction of change in each of these variables, which is considered to result in an improvement in product performance.
Picture 9 – Indication of Technical Response fulfilling customer requirement
- The relationships matrix which relates them using any one of several distribution methods/inter-relationship (central)
This section forms the main body of the House of Quality matrix and can be very time consuming to complete. Its purpose is to translate the requirements as expressed by the customer into the technical characteristics of the product.
Its structure is that of a standard two dimensional matrix with cells that relate to combinations of individual customer and technical requirements. It is the task of the QFD team to identify where these interrelationships are significant.
Each combination of customer and technical requirement is considered in turn by the QFD team.
e.g. how significant is padding thickness in satisfying comfortable when ganging?
The level of interrelationship discerned is weighted usually on a four point scale (high, medium, low, none) and a symbol representing this level of interrelationship is entered into the matrix cell.
Picture 10 – Interrelationship between Customer Requirement and Technical Response
Each level of interrelationship weighting is assigned a score which the team should understand and agree to before completing this matrix.
e.g. High (9), Medium (3), Low (1), None (0)
The relative values of these weightings should be chosen to suit the individual QFD project and may be varied later to study their impact on the QFD exercise’s conclusions.
- Roof
The triangular “roof” matrix of the House of Quality is used to identify where the technical requirements that characterize the product, support or impede one another. As in the interrelationship section, the QFD team work through the cells in this roof matrix considering the pairings of technical requirements these represent.
For each cell the question is asked:
Does improving one requirement cause a deterioration or improvement in the other technical requirement?
Where the answer is a deterioration, an engineering trade-off exists and a symbol is entered into the cell to represent this (usually a cross or “-“).
Where improving one requirement automatically leads to an improvement in the other requirement, an alternative symbol is entered into the cell (usually a tick or “+”).
Different levels of such positive or negative interaction (e.g. strong / medium / weak) can be indicated using different colored symbols.
Picture 11 – Checking relationship between Technical Responses
The information recorded in the roof matrix is useful to the design team in several ways. It highlights where a focused design improvement could lead to a range of benefits to the product.
Also it focuses attention on the negative relationships in the design. These can represent opportunities for innovative solutions to be developed which avoid the necessity for such compromises being made.
- Design Planning/Target Table (bottom room).
This is the final section of the House of Quality (HOQ) matrix to be completed and it summaries the conclusions drawn from the data contained in the entire matrix and the team’s discussions.
It is generally made up from three parts:
- Technical Priorities
- Competitive benchmarks
- Targets
Technical Priorities – the relative importance of each technical requirement of the product in meeting the customer’s specified needs, can be simply calculated from the weightings contained in the planning and interrelationship matrix sections. Each interrelationship weighting is multiplied by the Overall Weighting from the Planning matrix. These values are then summed down the columns to give a priority score for each technical requirement.
Picture 12 – Calculation of Technical Priority
Competitive Benchmarking – Each of the technical requirements that have been identified as important characteristics of the product can be measured both for the company’s own existing product and the available competitive products. This illustrates the relative technical position of the existing product and helps to identify the target levels of performance to be achieved in a new product.
Picture 13 – Competitor Benchmarking
Targets – the final output of the HOQ matrix is a set of engineering target values to be met by the new product design. The process of building this matrix enables these targets to be set and prioritized based on an understanding of the customer needs, the competitions’ performance and the organization’s current performance. The QFD team now needs to draw on all this information when deciding on these values.
Picture 14 – Setting Target
This is not necessarily the end of the QFD process. The output of this first HOQ matrix can be utilized as the first stage of a four part QFD process referred to as the Clausing Four-Phase Model. This continues the translation process using linked HOQ type matrices until production planning targets are developed. This approach allows the “Voice of the Customer” to drive the product development process right through to the setting of manufacturing equipment.
Picture 15 – Clausing Four – Phase Model
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