As we cover Six Sigma Statistics, I want to make sure that I go over the illustrative part of the statistics. We know Six Sigma is technical but the key to making it stick, is to make it simple and understood by the non-technical people using it. So let’s talk about the Box Plot or the Whisker Plot. A key thing to remember in Six Sigma is that everyone using different terminology, so ask questions and make sure you are speaking the same language.
What is a Box Plot?
Simply put a box plot helps to put a picture to the data showing you where most of the data falls, how the data is distributed and where the outliers are. So it basically shows you what you’ve got, how it looks and what is unusual about it.
What does it measure?
Say you have a process that has multiple variables affecting it and you want to know what is what. If you have a delivery truck with 4 alternative routes a box plot can show you which ones, according to the data, are the most problematic. Additionally a box plot will tell you how symmetrical your data is. Knowing if your data is skewed or not can affect how you interpret your data. In a box plot, if the data is mostly symmetrical the median will appear in the middle of the box and the whiskers will appear to be mostly the same length. IF the data is skewed to one direction, the median will not be in the middle and the whiskers will be different sizes.
How does it work?
Box plot measurements are based on quartiles and the distributions are shown within the graphic. Think back to your SAT’s or ACT’s. Remember how they told you that you scored in the 25th percentile? Well that’s a box plot. You will have an upper limit and a lower limit and those limits will be determined by your organization’s goals. The outliers will be the extreme values, values that are so far outside of the normal distribution that it is unlikely they will be reproduced.
Interpreting your data is just as important as gathering it, so choose carefully and with purpose. Talk to your belt and use that advice to help you find the best method for your organization.
In Six Sigma we are always collecting data, generally we are collecting data to address a current problem in our operations or services. The wonderful thing about Six Sigma is that we are also able to collect passive data. The usefulness of passive data is that it provides us with the ability to identify patterns, the catch to visualizing these patterns is in selecting the right graph to view the data.
Why use a graph?
The first benefit that comes to mind is the ability to see the error trends from a visual perspective. The other reasons graphs are a great tool are:
- Alongside identifying trends, they also help you see potential variable relationships. When you have a situation that could have multiple culprits, a graph can help you see which ones are a real potential.
- They can help you identify the risks that your customers will determine critical. This move allows your customer to be proactive instead of reactive, a much more desirable trait.
- It allows you to systematically dismiss variables and determine which one’s control other ones.
- It shows you the results of the passive data you’ve collected.
Where do I get the information for a graph?
Data is everywhere right? Yes and No. Your graph is only as good as your data, so we don’t want questionable data. The integrity of your data will be defined by your individual organization, but if you stick to these three questions you should be fine:
- What do you need the data to tell you?
- How often do you need to collect it?
- How do you need to collect it?
Next week we will get into the types of graphs and what times of data are appropriate for them. Until then happy hunting!
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.
In any lean project there are a ton of buzzwords, but the one thing that is a universal truth in all lean initiative is that for any tool used to be successful it must be understood. In today’s blog we are going to talk about a Gemba walk and why it works.
What is it?
A Gemba walk is literally seeing where the work happens and the value of work. The reason for the walk can be varied but its importance is to illustrate the process to the people who will be responsible for improving it. I like Gemba because it takes 6Sigma out of theory and metrics and illustrates it in a tangible way that makes sense to the people using it.
What do I do?
This is by no means a comprehensive checklist, but it is a place to start when you are planning your Gemba walk. I provided a simple but comprehensive checklist to create your Gemba walk below.
- Identify the processes (internal/external) that the customer pays for and has an expected output.
- Identify who understands the process- What you are looking for here is not the person/division/team responsible for the process, but the person who designed the process and understands why it operates the way it does. This person should understand the performance gap analysis and have a plan to correct the gap (or at least the beginning of an idea).This step is hard for a lot of people because the knowledge master generally isn’t the person with the official responsibility, but it is critical that you get this step right.
- Focus on the steps of the process that add value, show standardization or show how the work is distributed.
- Know the expected outputs-Are they gaps? Are you asking why? Are you assigning blame? (If are, you shouldn’t be.)
- Identify the areas of the process that are going well, what is making that success happen?
- Now that you know what is working and what is not, create your checklist based on this information.
- Remember to steer clear of the 3M’s and educated your process leaders on them. Muda-Waste, Mura-process variation not caused by the customer, and Muri-overburden on facility, people and equipment caused by Mura and Muda.
This is pretty comprehensive checklist, but as with all my posts this is just to introduce you to the Gemba Walk tool. Consulting with your belt will give you the most useful questions and sources of information in your walk. Done correctly a Gemba walk jumpstart rapid improvement events, done incorrectly they can derail an entire initiative. What will you value today?
Six Sigma is often thought of as a statistic heavy method and to some degree that is true. But the truth about statistics is if you don’t understand what they are trying to tell you, then they are just numbers on a page. The good news is that the purpose of Six Sigma metrics generally fall into 3 categories: can I make it better, can I make it faster or can I make it cheaper.
Basic Metrics Help Me Make It Better
These metrics are typically Defects per Unit (DPU), Defects per Million Opportunities (DPMO) and Rolled Throughput Yield (RTY). The purpose of these metrics is to decide whether you can eliminate waste and increase the quality of your end product. This is a metric that will not create an almost answer, you will identify and work from a root cause perspective.
Basic Metrics Help Me Make it Faster
This measurement deals almost exclusively with cycle time, this category is almost singularly concerned with reducing production and delivery time. Focus on the cycle time requires you to focus on the process from cradle to grave. You are looking very much to reduce variations and eliminate non value added activities.
Basic Metrics Help Me Lower Cost
This metric requires you to deal with the cost of poor quality (COPD). If this is a measurement that you are using, your purpose is to find out where the quality problem is, how much it is costing the organization and how to eliminate it.
This is a basic summation of how you will decide what type of metrics to use, next week we will go into detail about specific metrics. Knowing why you are measuring something and what you need those measurements to tell you is the most important part of your 6Sigma project. Your belt will be able to walk you through a specific measurement and offer advice as to whether or not it is the best metric to use.