Last week we talked about normal distribution in your data. This week let’s kick the conversation off with non-normal distribution. There are a few different types of non-normal distribution, let’s take a look.
Skewed data is quite simply, a data distribution that is not symmetrical. Usually the longest tail points should point in the direction of the skew. Here’s what a skew looks like
Natural limits-these are the limits of sample size. The problem with natural limits is that these natural limits can bias the estimation of results and in some cases ensure that there can be no specific correlation between the sample and the data field.
This is also known as artificial limits and it’s important to realize that limits are imposed by the person analyzing the data. Basically artificial limits set an arbitrary point for acceptable and not acceptable. Say you make 40 chairs and hour, your designer decides that any chair that doesn’t make a rating of 80 is unacceptable. That acceptable rating is completely arbitrary based on the designer’s standards.
Mixtures occur when data from different sources is expected to be the same and is different. Say you’re looking for error data from two cashiers Shift A credit card receipts and Shift B, cash receipts and the skew is not the same. You were expecting the error rate for each method to have a normal distribution and what you got showed something like this.
Next week we will pick up with a continuation of non-normal distributions. Until then, Happy analyzing
In this blog we have talked a lot about the different tools we can use in our improvement projects, but it’s my professional opinion that knowing why something works is as good as if not better than knowing that it works. In this blog post we need to discuss how you categorize defects. When you have enough data to cast a critical look over your process, you will find yourself face with the inevitable question of ‘how to I classify the variety of errors’? Well have no fear; here are the 3 most common classifications:
A controllable error or defect is something specific that you can pinpoint and directly affect with improvement. For example think of the lowering of the thermostat to improve the operating expenses or pressing the collate button on the copier to reduce the prep time for paperwork.
These are errors that occur during the steps of a process, like a safety checklist or a quality control checklist. The easiest way to decide if an error belongs in this category is to ask yourself ‘ is this a routine step to completing a task? If the answer is yes, then it’s procedural.
This is the trickiest category of all because it is basically a runoff category. This category is for things that cannot be fit into a specific setting or procedure. The category is for miscellaneous and arbitrary errors, think things like the amount of noise children make in school. If it is too big to measure and too hard to assess, it is most likely a noise classification.
The trickiest thing about 6Sigma is knowing which tool to use, to that end knowing where to classify potential areas of improvement is even more necessary. This is a great place to start and once you are ready to start categorizing your errors, we can help. Give us a call and we can you started.
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.
Process mapping is an excellent tool that doesn’t have to be monopolized by 6Sigma professionals. The best thing about a process map is the ability to illustrate the problem. Often times in an organization we understand that there is an issue, but we just don’t know what it is. Process mapping helps you to literally see the problem.
How does it work?
Like all things 6Sigma it can be as complicated or as simple as you would like for it to be, having said that there are a few steps that I think you should include in your mapping effort.
1. Define what you need to know.
2. Identify one process at a time and take the process from cradle to grave.
3. In the beginning, stick to linear maps and be sure to define decision points.
4. Identify if different departments/people participate in the process and define those elements.
What does it look like?
Bottom line –a process map should illustrate your steps and show your organization exactly where you are. When you know where you are, you know where to go. This is a minimum, but give us a call and we can help you with the specifics.