Interpretation & Calculations
Plotted statistic for the Np Attribute Control Chart
the number of items in a sample meeting a criteria of interest
where m is the number of groups included in the analysis.
UCL , LCL (Upper and Lower Control Limit)
where n is the sample size, np-bar is the Average count , and p-bar is calculated with the following Np chart formula:
The Np chart formula are easily calculated for you using our SPC software.
Learn more about the SPC principles and tools for process improvement in Statistical Process Control Demystified (2011, McGraw-Hill) by Paul Keller, in his online SPC Concepts short course (only $39), or his online SPC certification course ($350) or online Green Belt certification course ($499).