I had a chance to review two academic QFD publications (book and YouTube) that could mislead modern practitioners of QFD.
The first was a published book by three esteemed faculty members of a non-US university. Their book did challenge the all-too-familiar :4-Phase QFD model” from the early 1980s as being fraught with problems, but their solution was to go back to the wall-sized QFD matrices of the 1970s and their examples are still for a build-to-spec component and require some 36 steps to complete
Their Voice of Customer (VOC) begins with a request for quotation (RFQ) that assumes the customer is accurate, complete, and will not change their requirements. This assumes two fictions: 1) the project schedule and resource pool allow enough time to complete all 36 steps, and; 2) meeting the RFQ specs is sufficient to assure customer satisfaction when the product is delivered.
Most modern product development teams have neither the time, people, or money to fill out all 36 charts in this process. They also experience that customers make mistakes and just fulfilling their requirements is no guarantee the customer will accept the product. (See the newsletter "An Apple a day, keeps competitors away!")
The second story is a YouTube broadcast by a professor at a very prestigious technical university in the U.S. In this 40 minute lecture, he instructs his class on how to complete a House of Quality (HoQ). He equates the HoQ with QFD (even though Dr. Akao, founder of QFD, emphasizes that HoQ is not QFD).
The professor then instructs the students the same way as it was done in the early 1980s and unfortunately still taught in many six sigma and lean classes today as well as online QFD templates (free or paid downloads).
Most readers will recognize these steps, so rather than repeat them, let's correct them.
Correct Way: QFD and House of Quality (HoQ)
Neither the above mentioned book nor the YouTube lecture had anything on acquiring customer needs.
The book used the RFQ (request for quotation), while the university lecture just asked students what they wanted in the product (a car was the class example). The modern approach is to use Blitz QFD® which has at least 6-8 steps to acquire, analyze, and prioritize the customer needs before even beginning the House of Quality.
Professionals seeking for best practice QFD for their projects should consider the QFD Green Belt® Course, which includes modern QFD templates (VOC table, Maximum Value Table, Customer Process Modeling, Analytic Hierarchy Process, modern HoQ with correct math, etc.) that are complaint with the most up-to-date ISO 16355 Standard for QFD.
Jumping to the discussion of House of Quality (HoQ) matrix, we can improve on what both of these publications offer and bring it up to the 21st century. After all, you should expect that a method focused on improvement and new product development would have changed in the last 40 years! So let's redecorate our House.
Japanese letters: Demanded | Quality | Characteristics
an example of bad House of Quality using a roof structure that hinders technology innovation
The House of Quality (HoQ) gets its name from its shape (the matrix has rooms like a house) and the fact that both the rows and columns reflect "quality" and not other design dimensions such as reliability, cost, innovation, components, processes, etc. In the early 1980s, I translated from the original Japanese, the terms yokyu 要求 (demanded) hinshitsu 品質 (quality) for the rows, and hinshitsu 品質 (quality) tokusei 特性 (characteristics) for the columns. These terms were useful for parts manufacturers who were driving QFD in the US and Japan at that time (1960s-1980s). As QFD has grown in usage across a broad swath of industries, I now prefer the more neutral terms "customer needs" for the rows instead of demanded quality, and "functional requirements" in the columns instead of quality characteristics.
The rows of the House of Quality (HoQ) are customer needs. Other houses or matrices will have different data in the rows, but we're talking about the House of Quality as explained above. What are customer needs exactly? First, they are derived from Voice of Customer (VOC) but must be refined and analyzed before they can be entered into the House. In fact, in most QFD studies I have facilitated, VOC rarely gives true customer needs. This is because the sales and advertising messaging always talks about features, and engineers always talk about features, so customers assume this is the best way to communicate. Except that customers are not experts in product features.
In the above college lecture, the professor asked students what they wanted in a car. The responses were predictably MPG (miles per gallon fuel economy), safety, reliability, fast, big, and cheap. These are not "customer needs" but they are "product requirements." It is not the customer that should be fast, safe, and cheap, but the car. To get to the needs, ask the customer why they want these product features.
The customer needs should be structured using an Affinity and Hierarchy diagram, and the level of detail should be at least tertiary for any meaningful House (HoQ). Structuring is critical for accuracy of the later math as well as for discovering unspoken and latent customer needs.
Prioritization of customer needs is done by the customer. Ordinal scale numbers like 1-5 should NOT be used. The YouTube professor suggests using whatever scale you want and as many levels as you want. Wrong!
The well known Weber's Law of 7+2 suggests that humans make the most accurate judgments when given 5 or 9 levels of distinction. For later HoQ math, ordinal scale numbers do not have sufficient information to accurately calculate +, -, x, or / functions; only ratio scale priorities should be used, and Analytic Hierarchy Process (AHP) is the method Dr. Akao has been recommending since 1987. How any expert in fields like technology, quality control, or statistical methods can still use "abacus" math is beyond understanding in these days of computers.
Functional requirements should reflect what the product is or does without assuming a design or solution. This strengthens later innovation steps because you have not locked your thinking around one paradigm. Functional requirements should also be structured with the Affinity and Hierarchy diagrams due to the later math steps.
The "roof" (the top triangle in the image) of the House of Quality was never a standard room. It actually came from a Reliability Function Deployment study where the goal was to fix a known problem, not to design a new product. The positive and negative relationships will differ according to the design or solution paradigm, and thus should only be done later in the QFD study as a part of concept innovation and selection.
The relationships between customer needs and functional requirements can be expressed in symbols, numbers, or words. As per Weber's Law, it is recommended to use either 5 or 9 levels. The 3 classical Japanese symbols are too few to make an accurate judgment. The QFDI recommends the ISO cloud cover symbols (called Harvey Balls in Excel), ratio scale numbers, or the words from AHP. Numerical weights for these relationships should not be in ordinal scale but in ratio scale using AHP as explained above.
When cross tabulating the matrix math, you can preserve the accuracy of the customer priorities and the relationship strengths if you have used ratio scale numbers. If you use ordinal numbers as in both the new book and the YouTube, your results will have no meaning. All that work and no meaning! And the AHP solution is so simple!
Quality Planning table (right side room) for competitive assessment and targets. First, are the three standard categories of customer importance, competitive benchmarking, and selling point equally important on your project? Classical HoQ assumes they are, but we know that is not always the case, depending on the project deliverables (we did that in the first step of Blitz QFD®).
Second, how accurate is asking a customer to rate their perceptions on a 1-5 ordinal scale? Did you know you could ask them to measure their satisfaction using meaningful terms? For example, if your project was to designing a new flashlight and one customer need was "I can see where I am walking on a forest path at night," the customer could more meaningfully rate competitive lights as "3 meters in front" "5 meters" etc. Also, remember you cannot add, subtract, multiply, and divide ordinal scale numbers.
Design Planning table (bottom room) for competitive technical bench-marking and setting performance targets is the only useful output of the House of Quality and is skipped over completely in the YouTube. Like the quality planning table, you can use real metrics and not 1-5 ordinal ratings, and use AHP if you do any mathematical adjustments to the Functional Requirement weights.
So redecorate your House of Quality with a modern flair. Your team deserves it and your customers deserve it. The steps to redecorating the House of Quality for the 21st century are taught in the QFD Black Belt® course, and includes an Excel template.