!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> Streamline Training & Documentation: Seven Basic Quality Tools

Tuesday, November 27, 2007

Seven Basic Quality Tools

The American Society for Quality (ASQ), the organization that administers the Malcolm Baldrige National Quality Award, provides a wealth of information on quality concepts and tools at its Web site. (Some of the material is accessible only to ASQ members.)

As a starting point for exploring the ASQ resources, you might look at the outline ASQ provides of seven basic quality tools:
  • Cause-and-effect diagram — A tool that identifies many possible causes for an effect or problem and sorts ideas into useful categories. The diagram is drawn so as to illustrate the main causes and subcauses leading to an effect (symptom). It is also referred to as the “Ishikawa diagram,” because Kaoru Ishikawa developed it, and the “fishbone diagram,” because the complete diagram resembles a fish skeleton.
(click to enlarge)

  • Check sheet — A simple data recording device. The check sheet is custom designed by the user, which allows him or her to readily interpret the results. (Check sheets are often confused with checklists. A checklist is a tool for ensuring all important steps or actions in an operation have been taken.)

  • Control chart — A chart with upper and lower control limits on which values of some statistical measure for a series of samples or subgroups are plotted. The chart frequently shows a central line to help detect a trend of plotted values toward either control limit.

  • Histogram — A graphic summary of variation in a set of data. The pictorial nature of a histogram — showing the frequency with which different values, or ranges of values, occur — lets people see patterns that are difficult to detect in a simple table of numbers. (ASQ provides a tool (xls) for producing a histogram.)

  • Pareto chart — A graphical tool (bar chart) for ranking causes from most significant to least significant. It is based on the Pareto principle, which was first defined by Joseph M. Juran in 1950. The principle, named after 19th century economist Vilfredo Pareto, suggests most effects come from relatively few causes; that is, 80% of the effects come from 20% of the possible causes. (ASQ provides a tool (xls) for producing a Pareto chart.)

  • Scatter diagram — A graphical technique to analyze the relationship between two variables. Two sets of data are plotted on a graph, with the y-axis being used for the variable to be predicted and the x-axis being used for the variable to make the prediction. The graph will show possible relationships. Note, however, that the two variables can appear to be related, when they aren't in any direct way. Those who know most about the variables must evaluate whether or not the apparent relationship is real.

  • Stratification — A technique that separates data gathered from a variety of sources so that patterns can be seen. In the case of a process, the tool uses a graphical representation of the steps in the process to make it easier to understand. (AKA "flowchart.")
(Sources: The Quality Toolbox, 2nd ed., by Nancy R. Tague (ASQ Quality Press, 2004), p. 15; ASQ glossary.)