Tools to Measure & Display Quality Improvement Data

Plot the Output

• In the define phase of a Six Sigma project, use run charts or control charts to graphically represent the output of a process. A run chart is a line graph used to visualize process performance over time while a control chart is a line chart with upper and lower control limits used to gauge process stability over time. If the process is stable, interventions can be implemented and their effects systematically analyzed. If the process is not stable, the analyst must work to stabilize production before any systematic process improvements can be made.

Chart Process Flow

• Use process flow diagrams such as decision trees, spaghetti diagrams, SIPOC (Suppliers, Inputs, Process, Outputs, Customers) and Ishikawa in the define phase to outline the current state of a process. These diagrams help analysts identify bottlenecks in the process to specify areas where interventions may improve process efficiency. Subject matter experts should be consulted when designing flow charts, and operators working the process should agree that the flow chart accurately depicts the current state of the process.

Descriptive Statistics

• Explain the data using descriptive statistics such as the mean, median, mode, range, standard deviation and variance. Quality specific descriptive statistics include Process Capability Index (Cpk) and parts per million (ppm). Descriptive data are important both in the measure and analyze phases of a Six Sigma project. These statistics will tell you what the typical output of the process is and how often a process meets the specifications outlined by the customer.

Analyze the Data

• Once process improvement has been that implemented data is collected and analyzed to assess the effectiveness of the intervention. Statistics such as analysis of variance (ANOVA), t-test, regression and chi-square are commonly used during the analysis phase of a Six Sigma project to compare the output of a process before and after an intervention was implemented. Control and run charts can be used to visually depict process improvements.