Category: Control Charts

What is Common Cause Variation? Common cause variation is the kind of variation that is part of a stable process. These are variations that are natural to a system and are quantifiable and expected. Common cause variations are those that are predictable, ongoing, and consistent. Major changes would typically have to be made in order […]

Have you ever wondered why your doctor may keep you waiting in the waiting room or why you have to fast before doing a blood test? Let’s see if Lean Six Sigma can give you an answer.

Does your data from yesterday represent the current state of your process better than that from a month ago? How can you place more emphasis on it yet still make use of older data? That’s what the Exponentially Weighted Moving Average does. 

A box plot may seem like a simple tool, but as this example shows it can help reveal common and special cause variation that may not have otherwise been noticed. Be sure you’re looking below the surface to optimize your performance!

Are you hearing voices? If it’s in a business context, then there is nothing to worry about — and it might even be a good thing. Let’s listen in to the voice of the process and hear what it has to say.

A U chart is one of four quality control charts that engineers use to track variation in a manufacturing process. The other three typical quality control charts are the p chart (which plots the proportion of defective items, the c chart (which shows the number of defects), and the np chart (which shows the number […]

When you speak of subgrouping, it is usually in the context of constructing a control chart. Let’s explore the topic in a little more detail. Subgrouping is a technique used in control charts to group data into smaller, more manageable sets or subgroups. The purpose of subgrouping is to increase the sensitivity of the control […]

How do you know if your diet is working? You need to start with a baseline and then measure change from that. You should do the same for all your processes. From that process baseline, you can know whether your process is getting better, worse, or not changing. The term “process baseline” typically refers to […]

In-control is not referring to the behavior of your children. It’s about whether your process is exhibiting common or special cause variation. Let’s explore how this works.

Are all your organization’s problems and issues of equal importance? Probably not. How should you handle those that are the most critical and important? Let’s find out. A Key Business Issue (KBI) refers to a critical problem or challenge that your organization faces, which can significantly impact your performance, growth, or competitiveness. KBIs are specific […]

Since there is variation in all processes, how can you tell whether the variation is due to random expected variation, or something unexpected? The control chart is a tool for making that distinction. Let’s learn how that is done. 

Short production runs are a necessity in high-mix, low-volume manufacturing environments. The trend in manufacturing has been toward smaller production runs, with production runs – as well as products – tailored to the individual customer’s needs. Although this minimizes inventory and improves responsiveness to the customer, it complicates the application of statistical process control (SPC). Classical […]

The run chart is a powerful, simple and easy-to-use process improvement tool. Often, the run chart is shortchanged as the statistical tests that can be used with run charts are overlooked. This article takes the reader through the benefits of a run chart as well as how to correctly create and analyze one. A process […]

Every process falls into one of four states: Ideal: produces 100 percent conformance and is predictable Threshold: predictable but produces the occasional defect Brink of chaos: not predictable and does not produce defects Chaos: not predictable and produces defects at an unacceptable rate Processes tend to migrate toward chaos if not effectively managed. Pre-control Charts […]

Statistical process control (SPC) is the application of statistical methods to identify and control the special cause of variation in a process. Control charts, in theory, are used in product and process development to analyze processes. When a process is shown to be in control in both an average and range chart the process can […]

Multivariate analysis techniques may be useful in statistical process control (SPC) whenever there is more than one process variable. Multivariate control charting is usually helpful when the effect of multiple parameters is not independent or when some parameters are correlated. This article focuses on parameters that correlate when the Pearson correlation coefficient is greater than […]

Article authors, participants in discussion forums and even software documentation claim that  any data and especially time-sequenced data are useful only if they are homogeneous – that is, only if they display control chart stability (CCS).1,2,3,4 According to one quality control expert, Donald J. Wheeler, when out-of-control signals occur, “all of our computations, and all of […]

The recent spate of events such as rogue trading losses, flash trades and a seeming outbreak of Ponzi schemes has made many in financial services wary about their existing risk management practices. In post-financial crisis times, financial services companies are already under pressure to cut their operational costs while also being expected to comply with […]

Control charts have two general uses in an improvement project. The most common application is as a tool to monitor process stability and control. A less common, although some might argue more powerful, use of control charts is as an analysis tool. The descriptions below provide an overview of the different types of control charts […]

This article introduces the concept of earned value management (EVM) indexes, a project assessment technique, and control charts, a statistical tool for monitoring variation in a process, and describes how both may be used in tangent to capture more insight from project performance.  What to Know About EVM Indexes EVM is a project management technique […]

Statistical process control (SPC), despite sounding esoteric, is a subject that every process owner and worker should – and can – understand, at least at a high level. Knowing whether a process is in control and stable is paramount to producing a product or service that meets customer needs. In this hour-long Minitab training course […]

A true control strategy should be aligned with the process’s statistically based control limits.

To plot individual data or to group the data and plot the mean on a control chart, that is the question. Several authors (not including Shakespeare) have weighed in on this issue and I want to present their arguments and then my own. First, let us assume that the process conditions are such that using […]

From tedious time consuming task to opportunity for improvement. When applying control charts it is common practice to establish the control limits based on the process capability study and then use fix limits on the chart during production. This method is also frequently applied in SPC software programs. The advantage of using fixed limits is […]