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Quality and Process Methods > Control Chart Builder > Statistical Details for Control Chart Builder > Statistical Details for P, NP, and Laney P′ Charts
Publication date: 07/24/2024

Statistical Details for P, NP, and Laney P′ Charts

In Control Chart Builder, the lower and upper control limits, LCL, and UCL, respectively, are computed using the following formulas:

P chart LCL = Equation shown here

P chart UCL = Equation shown here

NP chart LCL = Equation shown here

NP chart UCL = Equation shown here

Laney P′ chart LCL = Equation shown here

Laney P′ chart UCL = Equation shown here

where:

Equation shown here is the average proportion of nonconforming items taken across subgroups

Equation shown here

ni is the number of items in the ith subgroup

K is the sigma multiplier and is set to 3 by default

σz is a moving range sigma calculated from the standardized values

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