An analysis method that measures planned and actual input and output for a linked set of resources to identify the source of disruptions in output. If the plan for a given work centre calls for 100 units/day of output and it is only achieving 80, I/O control identifies whether it is getting required input as planned (therefore the problem is at that work center) or is getting only enough input for 80 units, which indicates a problem in a feeder work center.