# Six Sigma Online

## The power of the central limit theorem

Throughout the last couple of articles, I have explained and illustrated that understanding the random sampling distribution (RSD) of a statistic is key to understanding the entire basis of inferential statistics. Which is just a fancy way of saying “avoiding career-terminating decisions.” This month I’ll show you how the central limit theorem is your best friend, statistically speaking.

## Random sampling distribution are really something delightful

Last month I wrote about how the random sampling distribution (RSD) of various sample statistics are the basis for pretty much everything in statistics. If you understand RSDs, you understand a lot about why we do what we do in hypothesis testing, inferential statistics, and estimation of confidence intervals. Understanding RSDs gives you a huge advantage as you seek to use data in business, so let's take a closer look.

## You must balance risk and benefits when determining acceptability.

So I thought I was done with measurement system analysis after my last column, but I just finished reading Don Wheeler’s June 1 column, “Is the Part in Spec?” and the first thing I thought was, “Well, that was… complicated and ultimately unhelpful in answering the article’s title question.” I like a diversity of viewpoints, but they have to make sense. Does Wheeler’s? Let’s take a closer look.

## Every answer to statistical problems lies within RSD

As I was teaching class the other day, I told the students I was going to reveal to them the one secret they needed to learn to understand every statistical test they would ever use. The secret was the one thing that would make statistics more of a reasonable science than a bunch of equations to memorize, the one thing they needed to pass my class. (OK, there is a lot more needed to pass the class, but without this one thing doing so is a lot harder.)

## Destructive Gauges and Measurement System Analysis

We have recently covered a lot of ground on the topic of measurement system analysis (MSA). We talked about the basics of MSA, the potential study, the short-term study, and the long-term study. At this point you should have a pretty firm foundation in the importance and methods of good MSA studies for your research and production, as well as a practical tool to help you in doing measurement system analysis—the file "MSA Forms 3.22.xls" (gauge repeatability and reproducibility worksheets)— which is a free download from Six Sigma Online. In this article, I am going to tie up some loose ends and then talk about a frequent question, “Is MSA even possible with a destructive gauge?”

# Digging out from a data blizzard

As I’m writing this, our first big snowfall of the year is piling up outside and it is –10°C (15°F). This brings to mind the many times my grandfather told me of how he walked to school in winter uphill (both ways) with no shoes...

### News Flash

Six Sigma's lead instructor Steven Ouellette wrote an article with Dr. Jeffrey Luftig on "The Decline of Ethical Behavior in Business."

Six Sigma Online's lead instructor Steven Ouellette was profiled in the June 2008 issue of Quality Digest magazine. If you want to learn more about Steve's peculiar view of the world, as well as what he studied for a year in Europe, read the profile online.