dcsimg
 

Project Tools

Blog posts and articles about tools and techniques that help keep Lean and Six Sigma projects on track.

In my last post, I discussed how a DOE was chosen to optimize a chemical-mechanical polishing process in the microelectronics industry. This important process improved the plant's final manufacturing yields. We selected an experimental design that let us study the effects of six process parameters in 16 runs. Analyzing the Design Now we'll examine the analysis of the DOE results after the actual... Continue Reading
I used to work in the manufacturing industry. Some processes were so complex that even a very experienced and competent engineer would not necessarily know how to identify the best settings for the manufacturing equipment. You could make a guess using a general idea of what should be done regarding the optimal settings, but that was not sufficient. You need very precise indications of the correct... Continue Reading

7 Deadly Statistical Sins Even the Experts Make

Do you know how to avoid them?

Get the facts >
P values have been around for nearly a century and they’ve been the subject of criticism since their origins. In recent years, the debate over P values has risen to a fever pitch. In particular, there are serious fears that P values are misused to such an extent that it has actually damaged science. In March 2016, spurred on by the growing concerns, the American Statistical Association (ASA) did... Continue Reading
Like so many of us, I try to stay healthy by watching my weight. I thought it might be interesting to apply some statistical thinking to the idea of maintaining a healthy weight, and the central limit theorem could provide some particularly useful insights. I’ll start by making some simple (maybe even simplistic) assumptions about calorie intake and expenditure, and see where those lead. And then... Continue Reading
After my husband’s most recent visit to the dentist, he returned home cavity-free...and with a $150 electric toothbrush in hand.  I wanted details. It began innocently. His dreaded trip to the dentist ended in high praise for no cavities and only a warning to floss more. That prompted my programming-and-automation-obsessed husband, still in the chair, to exclaim, "I wish there was a way to automate... Continue Reading
You have a column of categorical data. Maybe it’s a column of reasons for production downtime, or customer survey responses, or all of the reasons airlines give for those riling flight delays. Whatever type of qualitative data you may have, suppose you want to find the most common categories. Here are three different ways to do that: 1. Pareto Charts Pareto Charts easily help you separate the vital... Continue Reading
What is an interaction? It’s when the effect of one factor depends on the level of another factor. Interactions are important when you’re performing ANOVA, DOE, or a regression analysis. Without them, your model may be missing an important term that helps explain variability in the response! For example, let’s consider 3-point shooting in the NBA. We previously saw that the number of 3-point... Continue Reading
While the roots of Lean Six Sigma and other quality improvement methodologies are in manufacturing, it’s interesting to see how other organizational functions and industries apply LSS tools successfully. Quality improvement certainly has moved far beyond the walls of manufacturing plants! For example, I recently had the opportunity to talk to Drew Mohler, a Lean Six Sigma black belt and senior... Continue Reading
There's nothing like a boxplot, aka box-and-whisker diagram, to get a quick snapshot of the distribution of your data. With a single glance, you can readily intuit its general shape, central tendency, and variability. To easily compare the distribution of data between groups, display boxplots for the groups side by side. Visually compare the central value and spread of the distribution for each... Continue Reading
If you need to assess process performance relative to some specification limit(s), then process capability is the tool to use. You collect some accurate data from a stable process, enter those measurements in Minitab, and then choose Stat > Quality Tools > Capability Analysis/Sixpack or Assistant > Capability Analysis. Now, what about sorting the data? I’ve been asked “why does Cpk change when I... Continue Reading
In my time at Minitab, I’ve gotten a good understanding of what types of graphs users create. Everyone knows about histograms, bar charts, and time series plots. Even relatively less familiar plots like the interval plot and individual value plot are still used quite often. However, one of the most underutilized graphs we have available is the area graph. If you’re not familiar with an Area... Continue Reading
In an earlier post, I shared an overview of acceptance sampling, a method that lets you evaluate a sample of items from a larger batch of products (for instance, electronics components you've sourced from a new supplier) and use that sample to decide whether or not you should accept or reject the entire shipment.  There are two approaches to acceptance sampling. If you do it by attributes, you... Continue Reading
Now that we've seen how easy it is to create plans for acceptance sampling by variables, and to compare different sampling plans, it's time to see how to actually analyze the data you collect when you follow the sampling plan.  If you'd like to follow along and you're not already using Minitab, please download the free 30-day trial.  Collecting the Data for Acceptance Sampling by Variable If you'll... Continue Reading
In my last post, I showed how to use Minitab Statistical Software to create an acceptance sampling plan by variables, using the scenario of a an electronics company that receives monthly shipments of LEDs that must have soldering leads that are at least 2 cm long. This time, we'll compare that plan with some other possible options.  The variables sampling plan we came up with to verify the... Continue Reading
Earlier, I shared an overview of acceptance sampling. Now we'll look at how to do acceptance sampling by variables, facilitated by the tools in Minitab Statistical Software. If you're not already using it and you'd like to follow along, you can get the free 30-day trial version.  In contrast to acceptance sampling by attributes, where inspectors make judgment calls about defective items,... Continue Reading
If you're just getting started in the world of quality improvement, or if you find yourself in a position where you suddenly need to evaluate the quality of incoming or outgoing products from your company, you may have encountered the term "acceptance sampling." It's a statistical method for evaluating the quality of a large batch of materials from a small sample of items, which statistical softwar... Continue Reading
Many of us have data stored in a database or file that we need to analyze on a regular basis. If you're in that situation and you're using Minitab Statistical Software, here's how you can save some time and effort by automating the process. When you're finished, instead of using File > Query Database (ODBC) each time you want to perform analysis on the most up-to-date set of data, you can add a... Continue Reading
Not long ago, I couldn’t abide statistics. I did respect it, but in much the same way a gazelle respects a lion. Most of my early experiences with statistics indicated that close encounters resulted in pain, so I avoided further contact whenever possible. So how is it that today I write about statistics? That’s simple: it merely required completely reinventing the way I thought about and approached... Continue Reading
There are many reasons why a distribution might not be normal/Gaussian. A non-normal pattern might be caused by several distributions being mixed together, or by a drift in time, or by one or several outliers, or by an asymmetrical behavior, some out-of-control points, etc. I recently collected the scores of three different teams (the Blue team, the Yellow team and the Pink team) after a laser... Continue Reading