A free online reference for statistical process control, process capability analysis, measurement systems analysis, control chart interpretation, and other quality metrics.
ttributes capability measures are taken directly from attributes control charts. No additional calculations are required.
The capability for a p-chart is the average proportion of nonconforming items (p-bar). The capability for an np-chart is the average number of nonconforming items generated by the system (np-bar). The capability for a c-chart is the average number of nonconformities per subgroup (c-bar). The capability for a u-chart is the average number of nonconformities per unit (u-bar).
A weakness in capability estimates for attributes data is that they do not suggest why a system is either capable or not. For instance, there is no way of knowing whether the system is incapable because it is not centered, it is too close to a specification limit, or it exhibits too much unit-to-unit variation. Further studies must be done to learn how to improve the system.