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Six Tools from Six Sigma

Last week, we looked at the over-arching process used for correcting and improving within Six Sigma, DMAIC (Define, Measure, Analyse, Improve, Control).  DMAIC and Six Sigma are supported by a huge toolkit of quantitative and qualitative tools to support measurement and analysis.  Not all of them need advanced statistics or sophisticated training to use with some benefit.

Any competent manager should be building your own personal toolbox and here are six that can be readily and widely applied.

Five Whys

A simple means to get to the root cause of a problem is to start with a statement of the problem and to ask ‘why?’  Then, starting with your answer, ask ‘why?’ again, and repeat until you can go no further.  Now you have a root cause.

Why five?  There is no magic to five, but it does seem that you rarely need many more stages and too few steps will usually only take you to an intermediate cause.  Five seems to be at the sweet spot for many problems.

Fishbone Analysis

Also known as the Ishikawa (after Kaoru Ishikawa) Method, this is another way to help find causes.  But its emphasis is on breaking down the multitude of causes to an effect.  You represent the outcome (often unwanted) as the head of a fish, and then show/facilitate identification of as many causes as possible, representing each as a fishbone.

Fishbone (or Ishikawa) Analysis Step 1

Some causes are sub-categories or root causes of another cause, creating ever finer fishbones.

Fishbone (or Ishikawa) Analysis Step 2

SIPOC Analysis

SIPOC analysis looks for the source of a problem or poor performance in one of five places, with the:

  1. Supplier
  2. Inputs
  3. Process
  4. Outputs
  5. Customer


The Five Cs or 5C Process

It does not get simpler, conceptually, than this.  This will help you stabilise, maintain and improve a process or work environment.

  1. Clear Out
    Get rid of clutter and non-essential assets, materials, processes.
  2. Configure
    Create a tidy and effective working space:
    ’a place for everything, and everything in its place’.
  3. Clean and Check
    Keep everything clean and use the cleaning process to spot damage, faults and abnormal conditions.
  4. Conformity
    Ensures that everything conforms to the standards that have been set.
  5. Custom and Practice
    Ensure that everyone knows and follows the rules, and understands what purpose they serve.

Box Plots

Box Plots are a good way to plot data to see the effects of variation.  Rather than plot single data points, representing an average, such as the average height data for boys, below…

Average Heights of Boys (WHO data)

We can plot the ranges of heights for most boys (70%) with a box and nearly all boys (94%) with the bars.  This allows us to see two ranges on one chart.  Use the box for the commonly occurring range and the bars for either the whole range or, as here, for all but the extreme outliers, as in the chart below…

Range of Heights of Boys (WHO data) - 3rd, 15th, 85th and 797th percentiles

Failure Modes and Effects Analysis (FMEA)

Perhaps the most complex and sophisticated tool here, so, in a nutshell, we examine every possible failure mode and assign it a score.  Scores over a certain threshold lead the failure to be considered ‘critical’.

The score, or ‘Risk Priority Number’ is given by:

RPN = Severity x Occurrence x Detection

The individual scores for severity (how bad the fault is), Occurrence (how frequently it is likely to occur) and Detection (how hard it is to spot prior to release to customer) are calculated separately according to standard tables.  Examples of these tables are on the DMAIC Tools website, here.

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The DMAIC Solution Process

In last week’s Pocketblog, we took an overview of the Six Sigma approach to process improvement, and left readers with the statement: ‘it is time for the most interesting bit: the practical tools that non-experts can apply to making simple improvements from day to day.’

For all of the levels of certification that practitioners can acquire, most of us can simply understand and apply six sigma’s tools to day-to-day projects, problem-solving and improvements without training, just by understanding the basis and applying our own good sense and intuition.  I am not arguing against the value of full training and certification, but it is a huge investment if all you want to do is fix a small issue.

Indeed, many of Six Sigma’s tools have a life of their own outside the methodology and have simply been co-opted in to provide strength in depth for practitioners’ toolkits.  Next week, we’ll do a round-up of some of these.  This week, we’ll focus on the beating heart of the Six Sigma methodology, the DMAIC Process.

The Beating Heart: DMAIC

DMAICDMAIC can be viewed as a problem solving process, but I prefer to think of it as a ‘solution process’ because it starts with defining the solution you need to find.

Let’s break it down:





Define the solution you need, in terms of: who it affects (customers, clients, colleagues, stakeholders), the process involved, and the extent of the process (whether it is the full process or a part of the process).  Choosing the right problem to solve is an important part of the Six Sigma process.  It means making best use of necessarily limited resources.  The Define stage ends with a team charter that sets out the scope and status of the project.


Six Sigma is nothing if not couched in mathematics and quantitative methods.  This gives it its robustness.  The second step in the DMAIC process is to measure the current performance level, to give a good baseline against which to evaluate improvement measures.  This is a good opportunity to talk about Six Sigma’s Xs and Ys.

A Y is a measure of output performance.  It is an effect of the process.  Motorola talked of Big Ys as the things that matter most to the business’s most critical  customers.  The Measure stage of DMAIC concerns itself with Ys.

An X is is a cause – a factor, variable or process element which can affect the outcome.  The Big Xs are the factor that have the greatest impact on Big Ys.


Now it is time to find the cause of any failing in performance.  At the Measure stage, we understood the performance (or Ys) – now we find what factors affect that performance (the Xs).  Six Sigma has collated a host of quantitative and qualitative tools to gather data for the Measure stage and to interrogate it for the Analyse stage.


An effect Y is some function of one or more Xs so, in mathematical speak:

Y = f(X1, X2, X3, …)

If you can understand what Xs are important and how to change them to improve Y, then you can implement valuable changes.  Having a strong philosophy of quantitative, evidence-based interventions, Six Sigma practitioners will always look for opportunities to conduct limited (low risk) trials to test the validity of their evaluation before a full implementation.


The final step is about evaluating and sustaining the improvements.  Practitioners will set up a regime to monitor and control the relevant X factors and monitor the resultant Ys.

… and one more step?

In the UK, the Six Sigma Group (training and consultancy) advocates an extended DMAICT process that I would wholly endorse.  Other organisations may, too.  The final step is…



Transfer what you have learned and the principles you have used to the operational staff who can then use this knowledge to maintain and further improve the processes.  This is very much a step that is essential for external consultants to offer, if they want to avoid client-dependency.  Of course, some consultants relish such a dependency, but transferring learning is more respectful, more sustainable and, ultimately I believe, more reputation-enhancing.

Learn More: References on the Web

The best website I have found, by far, is iSixSigma.  It is a commercial site offering many related services, with free membership if you want additional information like newsletters.  It has a lot of valuable articles and a Six Sigma dictionary. is an online Six Sigma training business that also has a lot of freely accessible resources on its website.  The link will take you to the Knowledge Center (US Site).

My third recommendation is DMAIC Tools – another site with a wide range of free resources to help you learn about aspects of Six Sigma.  As its name suggests, this has a big focus on the tools and especially has a good coverage of the statistical side of the methodology.

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