Interpretation & Calculations
Plotted statistic for the U Attribute Control Chart
The average count of occurrences per unit of a criteria of interest in sample of items
where nj is the sample size (number of units) of group j.
where nj is the sample size (number of units) of group j, and m is the number of groups included in the analysis.
UCL , LCL (Upper and Lower Control Limit)
where nj is the sample size (number of units) of group j and u-bar is the Average percent.
The U chart control limits vary for each sample based on its sample size, but are easily calculated 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).