Attribute Control Charts – P and NP Charts

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This guide provides instructions on creating P and NP attribute control charts. P charts are often used to plot the proportion of nonconforming (defective) items per subgroup, while NP charts are often used to plot the number of nonconforming items p er subgroup.

P Charts

1. From an open JMP^® data table, select Analyze > Quality and Process > Control Chart > P Control Chart
2. Select one or more continuous variables from Select Columns, and click Process.   
3. Select the column defining the number of trials (i.e, sample size) for the n Trials role. Click OK. Note: If sample sizes are not constant, the control limits will vary. 

NP Charts

1. From an open JMP data table, select Analyze > Quality and Process > Control Chart > NP Control Chart
2. Select one or more continuous variables from Select Columns, and click Process.   
3. Select the column defining the number of trials (i.e, sample size) for the n Trials role. Click OK.    

Tips:

• The process variable must be sorted in time order.
• Many options, such as tests for special causes and capability analysis, are available from the red triangles.

Washers.jmp (Help > Sample Data Folder > Quality Control)

Visit Quality and Process Methods > Legacy Control Charts in JMP Help to learn more.