Exclusive Content & Downloads from ASQ

Use of Boxplots for Process Evaluation

Summary: The use of boxplots in place of single points in a quality control chart can provide an effective display of the information usually given in X-bar and R charts, show the degree of compliance with specifications and identify outliers. An example from a process evaluation illustrates the use of the proposed boxplot chart and compares it to the customary X-bar and R charts. To achieve a degree of robustness, the present paper compares several resistant measures of location and dispersion in terms of their efficiency for data from the normal, double exponential and "one-out" distributional situations. The results indicate that the mean and range of the middle half of the sample (suitably defined) combine to yield a boxplot chart with good statistical properties. For each pair of location and dispersion measures studied, a table gives the necessary factors to construct control limits.

Anyone with a subscription, including Site and Enterprise members, can access this article.

Other Ways to Access content:

Join ASQ

Join ASQ as a Full member. Enjoy all the ASQ member benefits including access to many online articles.

Subscribe to Journal of Quality Technology

Access this and ALL OTHER Journal of Quality Technology online articles. You'll also receive the print version by mail.

  • Topics:
  • Keywords: Control charts,Graphical methods,Outliers,Resistance
  • Author: Iglewicz, Boris; Hoaglin, David C.
  • Journal: Journal of Quality Technology