Last week we talked about understanding data and to continue with that thread, I want to talk about the specifics of collecting data. There are a few things to consider when you are deciding how to capture your data and before you make a decision consider these questions:
- What part of your business is making the requirements? Are you responding to customer service issues? Are you responding to due diligence requirements or compliance issues? Are you redesigning a product?
- How stable are the requirements? Is this a validated process or is it likely to change in the near future?
- How does your staff understand the process? Is information relayed directly to the personnel using the process or is it a trickle down environment?
Before you even begin to consider how to change the way you collect your data, you have to understand how it’s currently being done. The first thing to think about during capability studies is that when a capability study is conducted all of the information is included in the sample data; because of this you need to have a good understanding of short-term data and long-term data.
Short term data
- Is data that is collected during a very short, very specific period of time. For instance you may be looking for the errors that occur during the late shift on Wednesday.
- Is generally free of special cause variation.
- Commonly represents best case performance.
- Generally has more than 30 data points.
- Collected for a longer period of time, usually monthly or quarterly, through various periods of time.
- Contains common and special cause variations.
- More accurate representation of performance.
- Generally has more than 100 data points.
Understanding the way you collect data helps you make the most accurate analysis and leads to more refined business decisions. Understanding data can give you the tools to empower your employees in a meaningful way, taking the emotion out of business and offering a chance for data driven decisions.
One of the key things learnt from 6Sigma is the ability to accurately measure and analyze the information your organization collects. This can be as technical or as general as your organization needs, the key is to understand the level of specificity your organization needs and analyze from there. A Black belt will be able to give you in depth analysis, but a good one will give you exactly what your organization needs. We’ll start the discussion with Multi- Vari Analysis.
What is Multi-Vari Analysis?
Simply put this puts a face to the data. Once you have collected all of your information Multi-Vari studies take the data and illustrate the patterns of variation within the data. It helps you identify group or correlations between subgroups and over time. When you can identify the groups, you can make assumption or draw conclusions based on the data. For example if your data shows the your staff made more errors on product X you can draw the conclusion that your improvement efforts need to be focused on that particular product.
What is it used to assess?
Multi-Vari studies are useful in many ways but the most standard uses are
- to illustrate data in graphics.
- to show how work is influence by defined variables.
- to show the impact of specific material, departments or methods.
- the effects of external factors such as noise, delivery delays etc.
When you need to show stakeholders, influencers or project staff what you have found multi- vari studies are a great way to produce a visual. Since most people learn by doing, a visual representation allows them to see what they have done and to show leadership the gains or losses accordingly.
We opened last week with Process Capability and before we go full-fledged into that area, I want to pause and put some focus on capability studies.
What is a Capability Study?
To review from last week, a capability study is a way to ensure that your process is consistent over an extended period of time. For example if step 3 in your process produces 3 errors per cycle for 3 years, your process in consistent.
How Do You Find Stability?
There are a ton of tools you can use to test the stability of your process, but some of the most common tools are Time Series Plots and Control Charts. In addition to these tools there is a step by step process (of course!) to test the capability of your process, here they are.
What should know about capability studies?
As with all 6Sigma tools, the effectiveness of this tools lies more in how you understand and how you apply it. The most important things to remember are:
- Capability studies are used to measure the same parts of the process, at the same stage in the process at exactly the same time every time it is measured.
- You can use the capability study on discrete and continuous data.
- You get the best (ie most meaningful) information when you run the study on already stable and predictable data. New processes are not the best place for this tool.
- When you hear Sigma Level, they are talking about capability.
- Capability studies require you to understand:
- The limits of your customer or organization.
- The difference between short-term and long-term
data and what those differences mean to your organization or customer.
- Mean and standard deviation.
- How to assess normality of your data.
- How your organization or customer determine Sigma level.
Capability Studies can give you a great deal of insight on how your organization is running and what is making it difficult. This is one way to get a sense of the information flow and the quality of the information you can get your hands on. So let’s start off the new year with a look at what your data is telling you. Happy Hunting!
We’ve spent a fair amount of time learning the ins and outs of MSA’s, so this week I want to focus on process capability and how to understand the information you receive.
What is Process Capability?
In a nutshell Process Capability is:
• What it takes for your process to meet your customers’ needs right out of the gate with no modifications. This means for lack of a better term, inherent perfection.
• The information that can be provided on centering, variation and inappropriate measurement limits.
• The baseline metric for improvement
When determining your process capability there are three types of capabilities that we analyze:
• Continuous Capability- If you process is capable and in control, ideally you should get your desired outcome. This analysis measures the life cycle of your process telling you if the process has continued to be capable and in control.
• Concept of Stability-The idea of stability is the ability to answer the question ‘will my process produce the same result at this step every time it is used?’ To be technical, stability measures the ability of your process to meet its requirements at a regular and specific interval.
• Attribute Capability-This analysis makes assumptions about your data and is always long term data.
This week we’ve just scratched the surface on Process Capability. Next week, we’ll start digging a little deeper and show some illustrations of what it looks like.
We’ve talked about accuracy, repeatability and reproducibility in your MSA’s but now we need to talk about data integrity.
Numbers shouldn’t lie, but when they do it is usually because somewhere along the line the integrity of the data didn’t hold up.
Before you begin your analysis there are two questions you should ask yourself:
- Does my data have known reference points?
- Does the data match control documents? If you’re looking at product returns, does the data match the information on your financial documents?
Accuracy and Precision
The next thing to think about is accuracy and precision. When you are evaluating the accuracy of your data, what you are looking for is how close the average is to the anticipated value. Your precision will tell you how much variation occurs in you data. Think about it in terms of playing pool. Your accuracy tells you how close you were to making the shot and your precision shows you how far apart the balls were from the pocket.
The third thing to look at is any bias your data might have. Formally the definition of bias is the deviation of what was measured from the actual value. What that means is how far off your measurement is from the actual number. The goal is to reduce bias as much as possible, I say reduce because you will never be able to eliminate it. You will need to decide what acceptable bias limits are. If you have a worker who is consistently late and you’re measuring organizational tardiness, you know your bias is going be about 10 minutes.
Next you can move on to stability. Stability is defined as your error rate. The less errors, the more stable the process. All stability does is tell you when accuracy or bias changes in your process. What you should be looking for it to do is serve as an alarm, letting you know that something has changed. This alerts you to areas in your process that are no longer stable.
Last but not least, you have linearity. What this tells you is if your bias is consistent. If something happens once, it’s an outlier. It’s not consistent which means you don’t want to hinge a change or a new process on something that may or may not happen again.
MSA is a big subject and we are far from done with it. Next week we will continue to talk about MSA Windows in Minitab and how to interpret them. In the meantime if you have any questions give us a call and let us help!