iSixSigma

Sampling/Data

A Study of Estimates of Sigma in Small Sample Sizes

This paper looks at some of the methods of estimating standard deviation (which I will usually refer to as ‘sigma’). Additionally, I propose a new formula for estimating sigma for small sample sizes and also present a means to mathematically evaluate these competing estimates of sigma. The question was posed to me: “I have five…

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Use a Classification and Regression Tree (CART) for Quick Data Insights

In the Analyze phase of a DMAIC (Define, Measure, Analyze, Improve, Control) Six Sigma project, potential root causes of variations and defects are identified and validated. Various data analysis tools are used for exploratory and confirmatory studies. Descriptive and graphical techniques help with understanding the nature of data and visualizing potential relationships. Statistical analysis techniques,…

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Using Censored Data in Transactional Processes

Censored data is commonly used in reliability studies to determine the mean time to failure in order to establish warranty and maintenance periods for products. A large number of samples are subjected to either normal-use or accelerated-use conditions. Failure modes and occurrences are logged. Plotting the distribution of the sample failures over time allows the…

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How to Avoid The Evils Within Customer Satisfaction Surveys

When the Ritz-Carlton Hotel Company won the Malcolm Baldrige National Quality Award for the second time in 1999, companies across many industries began trying to achieve the same level of outstanding customer satisfaction. This was a good thing, of course, as CEOs and executives began incorporating customer satisfaction into their company goals while also communicating…

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VOC: Comparing Reactive Data and Proactive Data

Collecting data – be it voice of the customer or otherwise – requires a plan. Details of the plan should include what data to collect, how to get the information, where the information will come from and so on. Before any of these details are defined, however, the first step is to identify what a…

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Mind Mapping: A Simpler Way to Capture Information

Hospitals and health plans know that the high cost of care is squeezing the U.S. economy. That’s why so many of them are using Lean Six Sigma to control spending by refining internal processes – while still satisfying customers in a highly competitive market. A major health care consortium based in the Dallas-Fort Worth area…

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Process Data Mining: Partitioning Variance

Manufacturing facilities can be faced with major challenges when it comes to process improvement, largely because practitioners don’t always know enough about the underlying process factors (x’s) are that drive the improvement metric (Y). Practitioners might have a brainstorming session to tap into the collective experience of experts involved in the process, and design experiments…

Reducing Sampling Costs: Implementing a Variable Sampling Interval Strategy

Most manufacturing processes are controlled by sampling a product at some regular interval. Often, when a process is running normally, this interval is once every shift. It is not too surprising that in today’s economic climate, where cutting cost is of paramount importance, reducing sampling to save money is inviting, especially at large manufacturing facilities,…

Is There Bias In Your Random Sample?

By definition, a sample of size n is random if the probability of selecting the sample is the same as the probability of selecting every other sample of size n. If the sample is not random, a bias in introduced which causes a statistical sampling or testing error by systematically favoring some outcomes over others….

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Rounding and Round-off Rules

When performing statistical data analyses, quality professionals are always challenged to maintain data integrity. When should you round up the answer; when should you round down? How many significant figures are appropriate for the data set that has been taken? Below are a set of simple rules that should help you traverse the perils of…

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GE’s Six Sigma Focus On Span

We have heard about GE being one of the biggest proponents of Six Sigma, both for their own processes and for their customers. We’ve also heard how much GE has saved by implementing Six Sigma. This article is not a regurgitation of the existing rhetoric. Instead, I’d like to focus on an aspect of how…

Actionable Information from Soft Data

Engineers, Six Sigma practitioners and other researchers often work with “hard” data – discrete data that can be counted and legitimately expressed as ratios. But what of “soft” data, things like opinions, attitudes and satisfaction? Can statistical process controls (SPC) be applied here? Can process variation in customer satisfaction, for example, be measured and then reported to…

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How To Turn Process Data Into Information

A repeated series of actions and variables is a process. A collection of processes is a system. Virtually perfect Six Sigma quality results from an optimal interaction of all the variables in a given system. Process and system questions we all face at work include: Which variables are the most important to the customer? Am…

Digging for Data: Insurance Companies Strive to Improve

Based on experience with property and casualty insurers (P&C), one of the biggest profitability drivers is the expense incurred staffing and settling claims. Many P&C insurers struggle with timely and efficient claims processing. In working with P&C companies consulting groups found three common challenges that project teams must address to improve the overall claims settlement…

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Building a Sound Data Collection Plan

Black Belts and Six Sigma practitioners who are leading DMAIC (Define, Measure, Analyze, Improve, Control) projects should develop a sound data collection plan in order to gather data in the measurement phase. There are several crucial steps that need to be addressed to ensure that the data collection process and measurement systems are stable and…

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Enlist Process Owners to Survive an Absence of Data

The beauty of Six Sigma, over other decision-making strategies is that it is, by nature, data driven – it involves making decisions backed by evidence. In the absence of data, then, what good is Six Sigma? A Black Belt without data is like a navigator without a compass; finding north becomes complicated, but not impossible….

Eliminating the Fear About Using Confidence Intervals

One of the pleasures of teaching Green Belts is helping to eliminate the fear of statistical analysis. One technique is to place an emphasis on not only when and why a tool or methodology is used but also what the data says in “plain English.” Memorizing complex formulas may be the goal of many Master…

How to Determine Sample Size, Determining Sample Size

In order to prove that a process has been improved, you must measure the process capability before and after improvements are implemented. This allows you to quantify the process improvement (e.g., defect reduction or productivity increase) and translate the effects into an estimated financial result – something business leaders can understand and appreciate. If data…

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Improving Staff Scheduling at Providence Health System

As with most hospitals, labor is the largest budget expense at the Providence Alaska Medical Center (PAMC) in Anchorage. But benchmarking indicated that staff utilization at PAMC, a part of the Providence Health System, was above the 75th percentile of the national average. To remedy this, in October 2003, a multidisciplinary team (nursing, leadership, finance…

Basic Sampling Strategies: Sample vs. Population Data

Information is not readily found at a bargain price. Gathering it is costly in terms of salaries, expenses and time. Taking samples of information can help ease these costs because it is often impractical to collect all the data. Sound conclusions can often be drawn from a relatively small amount of data; therefore, sampling is…

Statistics Do Three Things – Describe, Compare and Relate

Fear of statistics is often a barrier to learning and applying Six Sigma methods. One way to minimize this fear is to remember that only three things can be done with statistics – describe, compare and relate. Many people are skeptical when they first hear this statement. “It couldn’t be that simple,” they think. However,…

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Sample Correctly to Measure True Improvement Levels

Many companies spend considerable amounts of money on customer surveys every year. They then use those survey results to amend strategies, design new products and services, focus improvement activities and to celebrate success. But can practitioners always rely on the results they see? Here is a fictional example: MyInsurance, a life insurance company with worldwide…

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Attribute Data: Making the Most of What’s Available

Six Sigma practitioners are aware of the range of numeric data types, from attribute data counts and tallies to continuous data measures on a scale. As the information strength in an element of data depends on the number of potential values it might take on, attribute yes/no data has to be considered the weakest. Many…

Stratification Leads to Specialized Improvements

Many times Six Sigma practitioners start projects or analysis at a broad level. These projects may include processing a patient through a clinical procedure, transferring medical records, registering a patient, or analyzing lab or equipment usage. In healthcare, the number of processes and their complexity can be very high; there may be thousands of processes…

Analytical Treatment of Discrete Ordered Category Data

Ordered category data is discrete data representing appraiser or client perception against a rating scale such as a survey or questionnaire. Black Belts learning to apply the Six Sigma methodology to ordered category data are traditionally taught analytical methods that include normal and Poisson distributions. This is probably due to Six Sigma’s beginnings in manufacturing….

Data Management Plans Can Reduce Project Cycle Times

Companion Article This is one of two articles by David Wetzel that explore the value of developing a data management plan as the intial step in the Measure phase of the Six Sigma DMAIC methodology. The other article is “Data Management Plans Can Improve Collection/Validation.” Long project cycle times, frequently cited as an impediment to…

Data Management Plans Can Improve Collection/Validation

Companion Article This is one of two articles by David Wetzel that explore the value of developing a data management plan as the intial step in the Measure phase of the Six Sigma DMAIC methodology. The other article is “Data Management Plans Can Reduce Project Cycle Time.” Understanding data and defining process paramaters (input) or…

Using Lean Six Sigma Measurement Tools in Maintenance

Lean Six Sigma is widely used in production, but it is just now breaking the surface in maintenance functions. Driving change in maintenance operations is a difficult task. Most maintenance personnel are taught on the job or learn their own techniques during the course of several years. Their experience in breakdown situations, which require them…

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Help for Project Leaders: ‘Advanced Data Door Worksheet’

Difficulties can arise in any phase of a Lean Six Sigma process improvement project, but one issue often shows up early in projects using the DMAIC (Define, Measure, Analyze, Improve, Control) model. When Black Belts or Green Belts charged with running an improvement project reach the Measure phase, they are confronted with the question: What…

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Margin of Error and Confidence Levels Made Simple

A survey is a valuable assessment tool in which a sample is selected and information from the sample can then be generalized to a larger population. Surveying has been likened to taste-testing soup – a few spoonfuls tell what the whole pot tastes like. The key to the validity of any survey is randomness. Just as…

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Why You Cannot Depend Totally on Statistical Software

The proliferation of do-it-yourself statistical software is giving some Six Sigma practitioners and other quality professionals, who are not strong in statistics, a false sense of confidence in their ability to collect and analyze data, and then reach sensible conclusions. What some may not realize is that much of the critical work is done long…

Use Cases and Measures: Strengthening the Six Sigma Link

“Use cases,” a term coined by Ivar Jacobson early in the evolution of object-oriented thinking, have been widely accepted as a helpful way to understand and document the functionality that is important in all kinds of software or business systems. Anyone within miles of object-oriented design will be familiar with the typical application of use…

Fast Start Collecting Data on Financial Service Process

In any financial service process that is being studied for the first time, it is common for Six Sigma teams to spend one-third to one-half of their project time on data collection alone. It simply takes a lot of time to figure out what data is needed, to develop a reliable data collection process and…

Using Vector Analysis for Turbo-Charged Data Mining

When the occasion requires it, there is often a better, faster path to Six Sigma results. Quality professionals can use the elegant theory that underlies Six Sigma statistical methods to turbo-charge projects. The underlying, unifying concept of turbo-charged Six Sigma is called vector analysis. When columns of measurements are treated as vectors, all of the…

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