Seven Quality Tools are a set of easy to use graphical and statistical tools that have been around for several decades. These tools were made famous by their effective use in Quality Control Circle (QCC) and hence have found their way into Lean Six Sigma programs. The seven tools are:
- Pareto Analysis is a vertical bar chart in which the bars are arranged in the descending order of their height starting from the left and prioritize the problems or issues. It is also known as the 80/20 Rule Analysis because it shows graphically that 80% of identified defects/failures are commonly caused by 20% of the identified issues. It is used to prioritize problems, analyze process output, identify root causes, etc.. It is a useful tool in all DMAIC stages.
- Flow Charts are graphical representation of steps in a process or processes within a system. It uses simple geometric symbols and arrows to provide a graphical picture of block sequences. It provides an overview of all the processes interactions and hence allowing for non-value processes to be identified along with other muda (waste). It is a useful tool in the Define, Analyze and Improve stages of DMAIC.
- Checklists is a list of actions or items that are required to be checked, inspected or verified. It is used to ensure things get done, information are remembered and acted upon without failure. In Lean Six Sigma there are deliverables and milestone checkpoints to be met. Using checklists to capture these for each stage of DMAIC is useful.
- Histograms is a graphical distribution of process data. It shows process variations and to determine process capabilities. Frequency histogram is an effective tool to visualize the spread of process data. From the shape of the histogram and a few simple statistical calculations will provide the parts per million (ppm) rejection value and the process Cp/Cpk. This tool is useful in the Analyze, Improve and Control stages of DMAIC.
- Scatter Diagram is a graph of plotted data points of two variable parameters. The distribution of plotted data points helps in identifying the cause and effect relationship between the two variable parameters. It graphically shows if the two variable parameters have a positive, negative or no correlation. This tool is useful in the Analyze and Improve stages of DMAIC.
- Control Charts are run charts with limits that are plotted over time. This is used to record data at a set time frames and sample size. These are then plotted on charts depending on the type of statistical formula used to determine the upper and lower limits and center of the run chart. The process can be analyzed and improved by evaluating these plotted points against their limits and their trends of plotted points. This tool is useful in the Measure, Analyze, Improve and Control stages of DMAIC.
- Cause-Effect Diagram is helpful in representing the relationship between an effect and the potential or possible causes that influences it. It is used during brainstorming sessions and to capture possible root causes to a problem in a graphical form. This tool is useful in the Define, Analyze and Improve stages of DMAIC.
These seven tools make up the common or fundamental tools that are used in Lean Six Sigma programs. Other QC and management tools are further added into a bespoke Lean Six Sigma programs based on the type of processes the organization has.