It is a common scenario: A practitioner has sales data for the past several months and wants to forecast next month’s sales volume. This type of forecasting can help manufacturers and distributors ensure they have enough product to meet customer demands. But how is this forecasting done? Statistical analysis software offers two ways to plot…
Measurement error is unavoidable. There will always be some measurement variation that is due to the measurement system itself. Most problematic measurement system issues come from measuring attribute data in terms that rely on human judgment such as good/bad, pass/fail, etc. This is because it is very difficult for all testers to apply the same…
Consider a production process that produced 10,000 widgets in January and experienced a total of 100 rejected widgets after a quality control inspection (i.e., failure rate = 0.01, success rate = 0.99). A Six Sigma project was deployed to fix this problem and by March the improvement plan was in place. In April, the process…
What is the usual way most people go about solving problems? Most people and organizations consciously or unconsciously use this method, as illustrated in Table 1 below. Table 1: Normal Method of Problem Solving Step Example 1. Understand what is to be improved and set a goal I am too fat. I want to reduce…
In some situations, Six Sigma practitioners find a Y that is discrete and Xs that are continuous. How can a regression equation be developed in these cases? Black Belt training indicated that the correct technique is something called logistic regression but this tool is often not well understood. An example about a well-known space shuttle…
The two-sample t-test is one of the most commonly used hypothesis tests in Six Sigma work. It is applied to compare whether the average difference between two groups is really significant or if it is due instead to random chance. It helps to answer questions like whether the average success rate is higher after implementing…
Three methods used to dissolve a powder in water are compared by the time (in minutes) it takes until the powder is fully dissolved. The results are summarized in the following table: It is thought that the population means of the three methods m1, m2 and m3 are not all equal (i.e., at least one m…
At its core, Design for Six Sigma (DFSS) is concerned with the accurate translation of what the customer wants into measurable characteristics, and then putting these characteristics into functions and design elements. The idea behind DFSS is intuitive and simple. If done well, a company will end up with a product that has what the…
The fishbone diagram is the most commonly used cause-and-effect analysis tool in Six Sigma. Cause-and-effect analysis is one of the key tasks in any Six Sigma DMAIC project because half of the game is won when the correct root causes of the problem (the Y) are found. However, poor use of the fishbone diagram is…
Estimating potential improvement project benefits unfortunately have not always been subjected to same level of analytical rigor that practitioners insist on applying in typical Six Sigma work. The fault lies in the lack of an analytical methodology. Project teams can help themselves over this hurdle with a straightforward method for calculating potential and actual benefits….
Well-focused improvements done in the right place can lead to significant system-wide results for an organization. In simple terms, it is a matter of choosing the right Six Sigma projects. But the problem is that it is not always easy to know which projects will produce the highest system-level leverage. Often Green Belts and Black…
In Six Sigma work, practitioners normally are expected to conduct a gage R&R study to verify that that the measurement systems being used are providing measurements free from variations due to repeatability and reproducibility problems. This is usually done in the Measure phase of DMAIC (Define, Measure, Analyze, Improve, Control) prior to data analysis so…
Everyone is taught in school the equation of a straight line: Y = a + bX Where a is the Y-intercept and b is the slope of the line. Using this equation and given any value of X, anyone can compute the corresponding Y. In Figure 1, Y = 3 + 2X. It is easy…
Lean government. The very idea sounds implausible. Even to the seasoned Lean practitioner, the idea of a Lean government sounds far fetched. Governments are traditionally seen as the epitome of bureaucracy, and the guardians of red tape, incomprehensible forms and endless queues. But there are workable Lean strategies for governments seeking to reduce waste and…
The DMAIC toolkit is excellent for solving technical complexity problems. However, Lean Six Sigma tools are not as adept at helping solve problems of high ‘people complexity.’ The solution is an integrated DMIAC/change management roadmap.
In any hypothesis test, there are four possible outcomes. The table below illustrates the only possibilities. Table 1: Possible Outcomes of a Hypothesis Test Reality Decisions Ho is true Accepting Ho is true; good decision (p = 1 – a or confidence level) Accepting Ho when it is false; Type II error (p = b)…
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