Dependence refers to any statistical relationship between two random variables. Correlation refers to any statistical relationship involving dependence. In a correlation study the six sigma practitioner would be looking for a correlation coefficient. The probability runs from -1 to +1. In other words, if two random variables are 100% correlated, the correlation coefficient would be +1 or -1. If there is no correlation, the correlation coefficient would be zero (0).
Critical to quality (CTQ) is the quality of a product or service in the eyes of the voice of the customer (VOC).
Use: It is a good idea to identify the critical to quality parameters as they relate to what is important to the customer at large. It is this author’s opinion that two things should be monitored—1.) the end-product parameters and 2.) And the associated process parameters that determine the quality of the end-product parameters that are important to the customer. Once these parameters are identified, the six sigma practitioner will want to monitor, control, and continuously improve upon these parameters.
Continuous flow is just that—the flow of value-add never stops. Ideally, a process would continue to add value without ever stopping during the production process.
Use: Lean practitioners should relentlessly strive for continuous flow through the reduction of waste. Any time a process stops, lead time is lengthened, the customer has to wait for the product or service, and it is costing more money than if the flow could be continuous in nature.
A critical to quality tree (also known as the CTQ tree) is a tool used to translate the needs of the customer (voice of the customer) into measurable product and process quality characteristics.
Use: To generate a critical to quality tree, begin by listing the customer’s needs, preferably in the customer’s own words. We proceed to refine these needs by asking pertinent questions about them until we have arrived at quality characteristics that can be measured (product and/or process).
Customers have needs and requirements. A customer need establishes the relationship between the organization and the customer (example: I need (or want) an iPad). Requirements are those characteristics that determine whether or not the customer is happy. (Examples: a requirement is that the iPad is user-friendly, has to be fast in data storage and retrieval, etc.)
Cycle time (also known as ‘process cycle time’) is the time from the start to the end of the process STEP.
Use: Cycle time is generally value-added time, but not necessarily. There can be some waste within cycle time which needs to be eliminated, or at least reduced. What the lean practitioner will do is add up all of the cycle times found on the value stream map and that sum is compared with the sum of the overall lead time. The ratio between the two tells you how efficient you are and most processes are less than 10 percent efficient. Many processes are even less than one percent efficient. That is not said backwards. Less than 10% of the time most processes are actually adding value.
The data collection plan consists of a nine column tactical plan. 1. Customer needs and requirements 2. Type of measure (input, output, or process) 3. …
For the most part, Six Sigma is taking broken processes and then fixing them. Six Sigma uses the DMAIC (Define, Measure, Analyze, Improve, and Control) approach; whereas, Design for Six Sigma (DFSS) uses a DMADV (pronounced DAH MAD VEE) approach. (Define, Measure, Analyze, Design, Verify) The more progressive organizations want to build into the design processes using a Six Sigma philosophy.
Design of experiments is a strategic and tactical approach to experimentation. With much of six sigma, we are waiting for assignable-cause variation to exhibit itself. With design of experiments, we are manipulating various factors (chosen by the cross-functional team) and manipulating them at different levels to see their effect on some desired result.
A defect location check sheet (also known as a defect map or a measles chart) is a structured, prepared form for collecting and analyzing data that provides a visual image of the item being evaluated so that data can be collected visually rather than with words. A common practice in quality assurance or even in six sigma is to count the number of defects found. One could keep track of the defect rate, and maybe even use an attribute chart to monitor, control, and continuously improve upon defect rates.
