I am dealing with a plant that has roughly 20 packaging lines, all fairly similar in design and so on. As part of our regular process, QC samples 6 bags from each line every hour and tests for leaks. Typically, the way the data are collected, they are pooled daily by line and a daily leaker rate (%) is determined. This results in roughly 14000+ bags being checked weekly. My question, is it valid to summarize the whole plant (20 lines) in a single pooled p-chart? Or is the only valid method to chart line-by-line?