Holistic Methodologies: Odd bed partners (Six Sigma and PMLC/SDLC), but Harmonious Relatives
Quality Function Deployment (QFD) - The House of Quality
Have you ever looked at your requirements catalog or product backlog and felt there were some missing pieces? Like you were searching for clues that would lead to a holistic set of requirements or the ability to show a graphical representation of them? This should not be a mystery or a whodunit. (Professor Plum in the Testing Lab with the Poison -- or was it the Lead Pipe?) In this article, we explore some clues and methods that you may not have thought about when working with your customer to pull together a set of diverse requirements.
In this series of articles, we have explored the use of various tools and methods specific to the DMAIC (Define, Measure, Analyze, Improve and Control) lifecycle for process re-engineering. A Quality Function Deployment, or QFD, is the foundation of process engineering or building a new process - DMADV (Define, Measure, Analyze, Design and Verify). While they look similar, DMAIC can be best characterized as an evolutionary change, whereas DMADV is more of a revolutionary change for a given process. In other words, one focuses on re-engineering an existing process, while the other is designed to help engineer a new process. In process engineering (DMADV), the use of a QFD starts in the Measure phase and builds through Analyze and Design. It is later used in Verify to validate requirements against the original process goal. The QFD and the SDLC intersect within the Requirements Catalog or Product Backlog.
In process engineering, the Measure phase focuses on gathering the customer needs and identifying what is critical to the customer (CTC) and also critical to the quality (CTQ) of the product. A QFD provides a method of capturing both CTCs and CTQs in a weighted relationship matrix, allowing the team many views into those interrelationships. Those views are characterized as "rooms."
Difference between Critical to Customer (CTC) and Critical to Quality (CTQ)
- CTC - Critical to Customer - These requirements are specific to what the customer is asking for in the product. For example, it can even be intangible such as color scheme or font on a screen layout.
- CTQ - Critical to Quality - These requirements are specific to reducing the defect opportunities in the product or when it is in use. For example: being consistent with date formats; following city, state, zip in an address block instead of putting zip before the city; incorrect tab order between fields creating more clicks or key strokes to get to the next logical field.
A CTC may or may not have any impact on a CTQ, however, common sense should prevail. Looking in detail at what is critical to the customer (CTCs) and what is critical to the quality of the product (CTQs) provides additional tools, leading to an appropriate design that can be tested using Failure Mode and Effect Analysis (FMEA).
Requirements Gathering and Validation
The QFD was created by Yoji Akao in the 1960s while working at Toyota, and was later used in the Mitsubishi Kobe shipyards. QFD was introduced into the US by Don Clausing of Xerox and MIT, with a later, independent introduction by Bob King of GOAL/QPC in 1985. The driving force of the QFD was to relate customer needs to functions and quality characteristics, with business processes or products delivered in mind. The QFD is indicative of the history of the Quality movement. Deming's original attempts to obtain traction in the US were unsuccessful, but Japan quickly adopted Total Quality Management (TQM) with the QFD being one of the many tools they added to the process engineering methodology.
How and Who?
A QFD is typically built by a cross-functional team of individuals who have been charged with responsibility for developing a new product, service, or process, or for refining an existing one. The team fills in a large matrix known as The House of Quality (HOQ) (in view of its shape). This HOQ then becomes the basis for a requirements catalogue of the complete set of customer and process needs, keeping in mind what is Critical to the Customer (CTC) and Critical to Quality (CTQ).
- Room 1. The Voice of the Customer/Process provides the Whats and represents the functional requirements provided by the customer. From left to right, it includes:
- An identification of high-level affinity groups which the VOC topics will fall within
- A list of the individual VOC topics (be sure to group them by priority within affinity)
- A prioritization rating - Scale 1-5. These values can also be summed and calculated as a percent of the sum total of the VOC Prioritization Rating. The resulting percent could be used instead of a prioritization rating scale of 1-5 (not included in this template).
- Room 2. Critical to Customer - Critical Customer Requirements (CCRs). This room at the top of the house contains two major sections:
- Hows are the quality characteristics of the What. The Hows, should be phrased to use performance measures which feed into the target values or specification. (These consist of broad topics or requirements of the product and are customizable for all types of applications whether they are products, services or processes.) For processes a QFD can be used in conjunction with a SIPOC.
- Goal - Desired direction of movement. What is better, higher or lower? Goal to minimize, maximize, or target the relationship between (Trend Up, Neutral or Trend Down).
- Room 3. Interrelationship or Impact Matrix grid - The cells in Room 3 contain the degree of correlation between the Whats and the Hows (Strong/Moderate, Weak, or no interrelationship or impact). They can also be represented using the symbols in the Correlation Matrix, but numbers are preferred to symbols in order to drive prioritization calculations. These relationships can also be represented as an impact interrelationship. (I have chosen a scale of 0-1-4-8 rather than the more traditional 0-1-3-9. I feel the gap between 3 and 9 seems too big given the difference between the other numbers in the series. But you can use your own scale as long it is used consistently.) Once relationships are noted and quantified, you can record the results in the sum column and row:
- Totals for What Importance in the column to the right. This matrix creates a weighted value based on the sum of each cell in a given row (VOC Prioritization Rating * Impact Rating).
- Totals for How Importance in the row at the bottom. Just sum each cell in a column (VOC Prioritization Rating * Impact Rating).
- Room 4. Competitive Analysis - Provides an interrelationship between other companies/teams, vendors or like processes. This "room" can be used to determine the level of change needed to retain a competitive advantage or keep the product being designed in line with the capability of other core processes. Another possible use is to compare your product as defined in Room 3 against a competitor to see where your product is on a maturity level. You could use either a scale of 1-5 using the current process as the baseline comparison, or "Competitor Rating" symbols to show the mapping between the vendors or comparison criteria.
- Room 5. Correlation Matrix (Roof) - The roof shows correlations between requirements, which are often overlooked and may indicate possible groupings of potential defects in an FMEA analysis. The correlation matrix can also be used to show the strength of an affinity between requirements, although I find this often hard to read when a QFD contains a lot of requirements.
- Room 6. Process Targets - These can be nonfunctional requirements such as performance, capacity, throughput, technical specifications, etc. that become the basis of KPIs or acceptance criteria for the given CCR.
- Room 7. Technical Evaluation results from the House of Quality - Can be customized to include:
- Fit gap, from best-in-class to unsatisfactory, Scale 1-5
- Level of effort or difficulty to implement, expressed in Story Points using a Fibonacci series or relative t-shirt sizes
- Total relationship value in column
- Weight/importance to CTC/CTQ
- Relative weighting you give to the model to drive priority
The performance measures in Room 6 can become the design specifications for the new product or service. When completed, the matrix calculations are used to reorder and prioritize these design specifications, directing the development team to concentrate their efforts on those specifications that really matter most in satisfying VOC, CCR and process needs.
An important side benefit of the QFD process is that it provides clarity for the team to think creatively about how to solve various system design problems and which metrics to put in place to be sure that they are evaluating their progress and efficacy correctly. It also provides a contract between the team members to agree on various subjective design criteria and their interrelationships.
QFD and Failure Mode and Effect Analysis
As mentioned earlier, there is a direct relationship between QFD and Failure Mode and Effect Analysis (FMEA). This relationship can be at the CTC or VOC topic level. For one example, see the template attached to this article. The template includes this comment: "The impact of cooling and power densities within a data center for a racked server that generates a lot of heat during operation or greater heat during malfunction could impact the performance or meantime between failure characteristics of other components in the same rack."
Usage within the PMLC/SDLC
QFD is a method of prioritizing and categorizing a requirements catalog using VOC and other criteria not often found in typical requirements catalogs or product backlogs. The various "rooms" in the QFD chart provide focus on aspects of requirement identification and decomposition that might not be inherent in the SDLC methodology:
- Including Voice of the Customer (VOC) and Voice of the Process (VOP*) in requirements
- Decomposition of high-level requirements by child QFD matrices -- Drives decomposition of requirements from Epics down to user stories (Agile) or nonfunctional core tenets, along with tasks or work packages within a WBS for waterfall
- Setting targets for acceptance criteria and initial design of test harnesses
- Showing clear linkage between VOC and CCR measures in the eyes of the customer
- Showing tradeoffs between conflicting or diverse requirements in Room 5 (Roof)
- Quantifying priorities -- importance to the customer or technical design criteria (CCR) depicted in a weighted scoring relationship between Whats and Hows
- Capturing an initial estimate of technical effort to deliver (story/function points) or classifying vendors from best-in-class down to unsatisfactory for a CCR as a result of a RFP/RFI
- Scoring against other industry/department or team peers relating to maturity and capability
If the PMLC/SDLC project is preceded by a DMAIC/DMADV project, a QFD should already exist. This tool can be used for scope validation and identification and preliminary Order of Magnitude (OOM) estimation and risk identification. This initial QFD can then be tied to a high-level Failure Mode and Effects Analysis framework that can be used to select a solution type.
This tool can be used in conjunction with -- or be the genesis of -- the requirements catalog and technical assessment, to look at the aspects of requirements listed in the bullet points above. QFD(s) can be a key tool for effort and resource estimation as well as ongoing risk identification, quantification and response. For vendor product selection it can be used to qualify RFP/RFI response analysis against CTC/CCRs.
In SDLCs where Design is part of Execute, determine if there are buried nonfunctional requirements that speak to the Voice of the Process (VOP), such as response time and process hardening, to avoid existing or resulting defects that can be incorporated as additional CCRs. Qualify the metrics you have identified in the technical evaluation when looking at design concepts to operationalize the product for the business process and customer (SLA). (A QFD can also prevent over-engineering of features that are not identified as important to the customer.)
Capture completed QFDs to use as templates for similar projects in the future. Build a historical database of requirements to use as future analogs for estimation or building on requirements that were not delivered in a given release. Estimates and updated actuals against target goals is beneficial historical information.
These measures could also be linked to the benefits realization gateway as a measure of meeting customer expectations (based upon attainment of the customer goals). These specification/target values should become your new baseline to show that the product is within specification when delivered by meeting them. The outcome of the requirements catalog can provide useful measures as input into control charts for tracking post-implementation benefits and confirmation of solving the initial business problem.
Limitations of QFD
QFDs are very complex interrelationship diagrams containing a wealth of information. To the untrained eye they can be very intimidating and overwhelming. Be sure that your audience is trained and mature enough to consume and garner value from this tool, or it may be perceived as a wasted exercise adding little or no value.
QFDs can be very time-consuming to create, and other than the Specification/Target values the values are highly subjective in nature and open to interpretation. However, the weighted average used in Room 3 tends to wash out any subjective bias over a large number of data points.
Using Excel, while the best tool, creates limitations with expandability of the "What's/How's" impact matrix (Room 3) in relationship to the roof interrelationship matrix (Room 5). Cells have to be redrawn if the number of CCRs is increased. The weighted average formulae for the Total Hows and Total Whats must be adjusted when adding rows and columns to the matrix. If your team decides to use QFD extensively, it will be much easier if you procure a professional tool. The template provided should be only considered a starting point for using a QFD within your SDLC projects.
The power of using a QFD is that it is highly customizable to your specific needs. You may find that only certain components or rooms are applicable to use for your specific needs, so it may not be necessary to completely fill out the rooms. QFDs can also be stratified or nested down to a very low level of detail and rolled up using the weighted values from the lower level QFDs into a summary QFD for consumption by the sponsor senior management.
Therefore you now have 7 rooms in the house of quality where Professor Plum could have "dunnit" with the lead pipe -- or perhaps a weighted VOC/CCR matrix, pick your poison -- which hopefully takes more of the mystery out of your requirements catalog or product backlog.
MIT video - https://www.youtube.com/watch?v=u9bvzE5Qhjk
Quality Function Deployment: How to make QFD work for you - Louis Cohen
Quality Function Deployment and Six Sigma Second Edition: A QFD Handbook - Joseph P. Ficalora and Louis Cohen