SPC Data Visualization of Seasonal Data

• Activity Number: 426
• Type: Contributed
• Date/Time: Tuesday, August 6, 2013 : 2:00 PM to 3:50 PM
• Sponsor: Quality and Productivity Section
• Author(s): Annie Dudley Zangi*+ and Diane K. Michelson
• Companies: SAS Institute and SAS
• Keywords: Statistical Process Control ; Control Charts ; SPC ; Time Series

Abstract

The periodic nature of some financial data makes it unsuitable in its original form for detecting anomalies using a SPC chart. One viable method for presenting this data on a SPC chart is to apply time series techniques first, then chart the output. This paper investigates a case study applying these techniques.

An equipment company was interested in monitoring monthly revenue, but the revenue figures were cyclic in nature, dropping off at the beginning of each year and peaking in December. While they could visually see the trend, months with unusual patterns were masked by all the months triggering alarms as traditional control charting methods failed to work.

SPC is beginning to be used more outside of manufacturing, in areas like banking, health care, and survey research, where the data may not be independent. In many of these environments, the desired mean may be shifting up or down, or the responses may be cyclic in nature. In this paper, we examine some of the problems with plotting time series data on control charts and suggest remedies.