Available analyses by measurement type

The appropriate quality analysis depends on the measurement type and the subgroup size.

In This Topic

Control charts and capability analyses for continuous data
Control charts and capability analyses for attribute data

Control charts and capability analyses for continuous data

Real-Time SPC creates control charts and capability analysis for process measures, output measures, and calculated measures.

Use Pareto charts when you have assignable cause and corrective actions to help focus your improvements efforts.

Control charts

Continuous data are often collected in subgroups. This means that more than one item is collected at the same time to represent the process.

Subgroup size = 1

When the subgroup size = 1, the appropriate control chart to use is the I-MR chart.

Subgroup size > 1

When the subgroup size > 1, the default control chart is the Xbar-R chart.

You can change the default control chart type when the subgroup size is > 1 according to your analysis goals.

Use an Xbar-S chart to monitor the mean and variation of a process when you have continuous data and subgroup sizes of 9 or more.
Use an I-MR-R/S chart to monitor the mean of your process and the variation between and within subgroups when each subgroup is a different part or batch.
Use an EWMA chart, which is a time weighted chart, to detect small shifts in the process mean, without influence by low and high values.

Capability analyses

Real-Time SPC provides the following continuous capability analyses.

Normal Capability Analysis: Use with the I-MR, Xbar-R, Xbar-S, and EWMA control charts.
Normal distribution with Box-Cox transformation or Nonnormal Capability Analysis: Use if your data do not follow a normal distribution.
For more information, go to When to use a nonnormal capability analysis.
Between/Within Capability Analysis: Use with the I-MR-R/S control chart.

Note

Only I-MR and Xbar-R charts and Normal Capability Analysis are available with Prolink measurements.

Control charts and capability analyses for attribute data

Real-Time SPC creates control charts and capability analysis for defectives, grouped defectives, and grouped defects. For more information, go to Defects and defectives.

Use Pareto charts to help focus your improvements efforts. Use Pareto charts to investigate the types of defects and defectives and the assignable causes and corrective actions. For more information, go to Pareto charts for defects and defectives.

Attribute data are also often collected in subgroups. The choice of attribute control chart depends on whether you collect defects or defective data and how you want to represent the data.

Note

You can monitor your defective count data separately, with one measure per control chart, or together, with several defective types on the same control chart. For more information, go to Quality attributes.

Poisson data - defects

When you count defects, the default control chart is the C chart and the appropriate capability analysis is a Poisson Capability Analysis.

You can change the default control chart type for your analysis. The main difference between C and U charts is the vertical scale.

Use a C chart to monitor the number of defects.
Use a U chart to monitor the number of defects per unit.
Use a Laney U' chart to monitor the defect rate for your process and to adjust for overdispersion or underdispersion in your data.

Binomial data - defectives

When you count defectives, the default control chart is the NP chart and the appropriate capability analysis is a Binomial Capability Analysis.

You can change the default control chart type for your analysis. The main difference between NP and P charts is the vertical scale.

Use a NP chart to monitor the number of defective items.
Use a P chart to monitor the proportion of defective items.
Use a Laney P' chart to monitor the proportion of defective items that are produced by your process and to adjust for overdispersion or underdispersion in your data.