Minitab Statistical Software Adds Laney P' and U' Control Charts

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Latest update to top statistical software adds tools designed to eliminate false alarms when monitoring processes.

Minitab® 16.2 Statistical Software adds new control charts that make it easier for quality improvement professionals to determine if a process is out of control.

Minitab® 16.2 Statistical Software adds new control charts that make it easier for quality improvement professionals to determine if a process is out of control.

Minitab 16.2 adds Laney’s P’ and U’ charts and an easy-to-use diagnostic tool that tells users whether or not these charts are appropriate for their data.

Minitab® 16.2 Statistical Software, an update to the most recent version of the leading software used for quality improvement and statistics education, adds new diagnostic tools and control charts that will make it easier to determine if a process is out of control.

The update is free for Minitab 16 users. The company also offers a free, fully functional, 30-day trial at http://www.minitab16.com

As any engineer knows, all processes have natural variation—but unusual variation may need attention. By graphing process data against an upper and a lower control limit, control charts help process owners recognize variation they should be concerned about.

But most people who’ve worked extensively with control charts, particularly attributes charts, have encountered “false alarms” where the control limits fell close to the mean and data points exceeded the limits even though the process was in statistical control.

The problem of false alarms due to overdispersion has been known since the 1950s, but a good solution didn’t exist until quality engineer David Laney proposed the P' and U' charts many decades later. Like traditional P and U charts, P' and U' charts are used to monitor defectives and defects, respectively. But where traditional charts assume a process defective or defect rate remains constant over time, P' and U' charts assume that no process exhibits a truly constant rate, and factors that into its control limits.

As a result, these charts can give users a more reliable indication of whether a process is truly in or out of control.

Minitab 16.2 incorporates Laney’s P' and U' charts as well as an easy-to-use diagnostic tool that tells users whether or not these charts are appropriate for their process data. “With these tools, quality practitioners across all industries can be confident about detecting special-cause variation only when it truly exists,” says Michelle Paret, Minitab product marketing manager.

Minitab worked directly with David Laney to incorporate the charts into this update. An extensive interview with Laney about the origin and theory behind the P' and U' charts is available at http://www.minitab.com/company/news/news-basic.aspx?id=10086.

Control chart false alarms can be caused by too much variation in process data, or “overdispersion,” especially if the data uses large subgroups. This situation creates artificially tight control limits, so points on a traditional P chart look like they’re out of control even when they are not.

Too little variation, or “underdispersion,” can also be problematic. Underdispersion can make control limits on a traditional P chart or U chart too wide, so data points that should raise concerns appear to be in control.

Whether a user's data exhibit overdispersion or underdispersion, a P' or U' chart will help distinguish true common cause versus special cause variation.

Minitab makes it easy to see whether a traditional P or U chart or a Laney P' or U' chart is more appropriate for a user's process data. The P Chart or U Chart Diagnostic in Minitab quickly tests the process data for overdispersion and underdispersion, and recommends the appropriate chart.

Minitab 16 was introduced in May 2010 and received rave reviews for its new functionality and features, especially the Assistant, a menu-based tool designed to guide users through their analyses and help them interpret their results with confidence.

Thousands of companies worldwide use Minitab to analyze data for quality improvement programs. More than 4,000 colleges and universities use Minitab for teaching and research.

Because it has been adopted by companies around the globe, Minitab 16 is available in English, French, German, Spanish, Simplified Chinese, Japanese, and Korean. Documentation is available in several other languages.

The company offers two other products. Quality Companion by Minitab® is process improvement software designed specifically to help professionals manage and execute quality improvement projects. Quality Trainer by Minitab® is an e-learning course that teaches statistics and serves as an ongoing resource for professionals who use statistics to implement quality improvement.

About Minitab

Minitab Inc. is the leading provider of software for Lean, Six Sigma and quality improvement projects. Thousands of distinguished companies use Minitab software, including Toshiba, DuPont, Boeing, Royal Bank of Scotland, Nestlé and Pfizer.

Minitab Inc. is headquartered in State College, Pa., operates offices in the United Kingdom, France and Australia, and has additional representatives throughout the world.

FOR MORE INFORMATION contact Eston Martz in Minitab media relations: PublicRelations(at)minitab(dot)com

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Eston Martz