As we continue our journey in Six Sigma it seems pertinent to discuss the different types of distributions you will see in your analysis. Let’s start with one at a time. The most common distribution is the Normal Distribution and here’s what you should know about it.
First, what is a distribution?
Simply put, a distribution will tell you how often a variable occurs in your process. This is important because the commonness of your variables will inevitable create a foundation for your improvement project.
Types of Distribution
The Normal Distribution
A normal distribution (Gaussian Curve, the average person knows it as the Bell Curve) shows a equal distribution. The mean (the average) divides the data in half, 50% on the data on each side of the mean. The Normal Distribution will have the following hallmarks:
This distribution is considered to be the most important distribution.
The area under the curve should equal 1.
Physical aspects of the curve should resemble a hill and should be symmetrical.
Both directions on either side of the mean extend indefinitely and never touch the horizontal axis.
White noise in your process should produce a normal curve shape
The Z distribution has a mean of 0 and a standard deviation of 1.
The mean (average), median (mid-point) and the mode (most common value) should be the same data value.
Next week, it’s on to non-normal classifications. Get to analyzing and if you need any help, reach out and let us know!
In metrics the most honest finding will be that your metrics will have degrees of variation. Understanding where and how those metrics occur, is the key to using your data in a forward thinking strategy. Let’s start with something simple, like toy production. We are going to track some standard variation sources.
Within Unit Encoding
This variation source occurs when you are measuring output from a single production cycle. Some places that variation is likely to occur are the width of parts, color shading, length of toy etc. Now you can choose to analyze different production cycles on the same day or alternating days, but you will always be comparing samples from the same cycle. A new production sample means a new data point.
Between Unit Encoding
These names are dead giveaways, but I digress! This implies that you are looking at samples from two different production cycles. This is different in that you would want to identify two different samples from different production cycles. The variations you are looking for will give you some clue as to whether the variations are operation influenced or process influenced.
This is the trickiest variation source. This specifically calls for you to compare your variation averages from all of your data points in a single day. So you can theoretically have both within unit variation data and between unit variations data, depending on how specific you need to get.
The key to getting the most out of your data is to understand what it’s telling you. Understanding where the variations are coming from is the first step to getting the most out of your data.
Okay for the last two weeks, I’ve been talking about Measurement System Analysis and before I move on to a new topic I have one final post on why you should be thinking about MSA. Here it goes…
Why you use it
- You use MSA to compare you customer’s expectations to your inspection standards. This is a very quick illustration of a value stream map and a good way to ensure that you are providing the best service for your customer.
- It gives you a snapshot of where the training in your organization should be.
- It gives you the opportunity to evaluate your trainers in a truly neutral fashion. The data doesn’t lie and you can assess the training in your organization from a truly objective perspective.
- Creates an opportunity to analyze your existing systems and evaluate new systems.
Why is it important?
- Allows you to measure the amount of variation in your measurement systems.
- Allows you to compare user variation.
- Allows you to compare two or more measurement systems.
- Helps you develop a baseline for measurement systems.
- Helps you develop a system to evaluate the moving pieces in your organization.
- Gives you a true before and after picture.
- Gives you a true measurement of variation and the causes of it.
- Evaluates your training programs.
So I am a big fan of MSA as you can tell, but the bottom line is that it can really affect your organization in the best way. It forces you to be accountable and it forces you to pay attention to the changes. Give it shot and if we can help, let us know.
This week we will continue our discussion on process mapping, I promise it will not go on forever, but it does have a lot of intricacies. Many people think that process mapping is just putting some shapes on a diagram, but it means much more than that. There are 3 levels of process mapping that are commonly accepted among the 6Sigma crowd.
Level 1 –The Macro Process Map
This is typically how management views the processes of the organization; it’s a big picture, future strategy kind of view. It also creates the ability for management to see how to position the organization or resources in a way that complements the product/service being created. This is a high-level map which generally includes:
- Activities that relate to one major process step
- How the process fits into the big picture
- Little specific detail
- Visualizes only major process steps
- Can be used with only a general understanding of the purpose of the process and its steps.
Level 2-Process Map
This is the worker bee process map, where the people who have specific knowledge of the process come in. This is the map that is used to identify all the major steps a worker takes to complete a process. Within Level 2, there are 4 types of process maps:
- Linear Flow- A straight line from beginning to end.
- Swim Lane-shows you who is responsible for what task.
- SIPOC-a little more complicated. It takes five areas: your suppliers, your inputs, your process, your outputs and your customers.
- Value Stream-a specific map that helps to visualize and understand the metrics for the performance of major steps.
Level 3-Process Flow Diagram
Level 3 is not a must because this is a micro process map. It is where you zero in on a specific area and focus on the steps in the process that are causing whatever challenge you are having. When beginning this level you need to ask the following questions:
- Which steps contributed to the problem?
- Where would the problem most likely have occurred?
- Are there elements to the product/service that lend itself to the problem?
These questions help you find the focus that you decided in your problem statement. For this to work you will have to break each step in the process down, most easily using SIPOC. Remember a Level 3 map should include:
- All process flows
- Any set points
- Any standard or automated procedures
- Inputs and outputs (specify if the are controllable or non-controllable)
- Defects per unit
- Yield and rolled throughput yield
- Value and non value added activities
It’s a lot of information, but mapping a process is a fundamental step in your improvement project. It is absolutely critical that you get it right. For more help or more information, give us a call and we will be happy to get you started.
6Sigma Tools: Process Mapping-Standard Symbols
As I said last week, process mapping is one of my favorite 6Sigma tools and the best thing about it is that anyone can do it. Now as with all things 6Sigma it can be as complicated or as easy as you want it to be. It may seem like process maps have a secret language, but this week’s blog helps you decipher the code.
What is it?
Rectangle illustrates an activity within the process. When activities are described in a rectangle they generally begin with a verb.
When you see a diamond, a decision has to be made. These decisions are generally yes/no or go/stop.
An arrow shows you which way the process is flowing and where it is connected.
A parallelogram shows that this step in the process is a data point.
An ellipse shows the start and ending of a process but some people like ovals or circles. I like circles myself, it really doesn’t matter but if you want to get technical ellipses are the Alpha and omegas of process maps.
Some people swear by MS Project or Visio, but the truth is that MS Excel or MS Word is just as effective for producing process map. The meat of this tool is that you illustrate the steps. I’ve provided an example of one of the process maps I designed for a client, when you first start mapping a process it’s better to focus on something simpler. This process is just an example of what a finished process map looks like.
What should it include?
At a bare minimum it should show how and where the process starts, who/what influences it (inputs) and the end goal/product. A more desirable map shows cycle times, value and non-value added tasks and activities, decision points, problems with immediate fix capabilities and process control needs. But that is not a hard and fast rule; your client will dictate what the map needs to show. As you can see from my process, my client wanted a “no-fluff” chart, a map that only illustrated the tasks that actually took place.
Why use it?
Aside from the clarity that comes with visualization, process mapping is good for:
- Visualizing improvement points
- Understanding root cause possibilities
- Complementing analytical tools with the data it provides
- Identifying what you will need to make improvements.
What doesn’t it do?
Every tool has its limitations and the process map does not give you a silver bullet. It cannot determine the level of variation, but it can determine if there is variation. It cannot stabilize your process but it can illustrate the best place to start looking for improvements. When you are ready to start giving your processes a deeper look, let SPC help get you started.